Electronic structure and optical properties of nitrogen-doped antimonene under biaxial strain: first-principles study.

CONTENT: In this thesis, the role of N atom doping and biaxial strain in modulating the electronic structure and optical properties of antimonene has been deeply investigated using a first-principles approach based on density-functional theory. The results show that N doping significantly reduces the band gap of antimonene and introduces new electronic states, thus affecting its electronic structure. In terms of optical properties, N doping reduces the static permittivity of antimonene and alters its absorption, reflection, and energy loss properties. In addition, biaxial strain further enhanced the modulation effect of these properties. This study not only provides theoretical support for the application of antimonene in the field of high-performance two-dimensional electronic and optoelectronic devices, but also reveals strain and doping as an effective means to modulate the physical properties of two-dimensional materials. METHODS: For the calculations, we used the DFT-based CASTEP software package for the simulation of the electronic structure. In order to more accurately characterize the weak interactions between two-dimensional materials, we specifically introduced the Van der Waals dispersion correction. We have chosen the Perdew-Burke-Ernzerhof (PBE) exchange-correlation generalization under the generalized gradient approximation (GGA) and combined it with the Van der Waals correction term in order to fully consider the electronic structure of antimonene. For the calculation parameter settings, we set the truncation energy to 400 eV to ensure the accuracy of the calculation. Meanwhile, we adopt a 6 × 6 × 1 k-point grid for Brillouin zone sampling to obtain more accurate energy band structure and density of states information. For the convergence settings, the convergence criteria for both the system energy and the interaction force between atoms were set to 1 × 10-5 eV and 0.01 eV/Å, respectively. We selected a 3 × 3 × 1 supercell model with 18 Sb atoms. A vacuum thickness of 18 Å was established in the Z direction, which is sufficient to avoid interactions between the two atomic layers above and below the periodic structure.

Adsorption of Zn atoms by monolayer WS2 doped with different atoms X (X = O, Se, N, P, F, Cl): first principles study.

CONTEXT: The effect of X (X = O, Se, N, P, F, Cl) doping on the adsorption of Zn atoms by WS2 was investigated based on first principles. The electronic structure and optical properties of the adsorbed system after atomic doping were calculated. It is found that the Zn atom adsorbed on the W top (Tw) site has the most stable structure. When an S atom is replaced with an X atom based on the adsorption system, where the adsorption energy decreases after doping of O, P, F, and Cl atoms compared to the undoped system, it means that each system is more stable after doping of these atoms; charge transfer shows that the adsorption system after P-atom doping the system around the Zn atom loses electrons while S-atom gains electrons, which indicates that P-atom doping is favorable for the adsorption of Zn by WS2, N, P-atom is introduced as p-type doping and F, Cl-atom is introduced undoped by n-type doping, and the band gap of the doped system is less than that of the undoped one. With the introduction of different dopant atoms, certain impurity energy levels are introduced into the adsorption system. The prohibited bandwidth around the Fermi energy level reduces the density of states, causing the doped system's density of states to shift to lower energies, among which the shifts of N, P, F, and Cl are more pronounced. The P-doped adsorption system shows a new peak near the energy of - 11 eV. In addition, the study of optical properties showed that the peak reflections of both doped and non-doped systems adsorbing Zn atoms appeared in the ultraviolet region; the absorbance coefficient of the doped system is moved in the lower energy direction and red-shifted after atom doping; in addition, the absorption coefficients and reflectance of the P, Se doped systems are enhanced in the wavelength range of 200-300 nm compared with that before doping, the dielectric function and CBM and VBM positions were also calculated further indicating the potential of Se-doped systems in improving photocatalytic efficiency. METHODS: In this paper, the structure optimization of X (X = O, Se, N, P, F, Cl) doping on WS2 adsorbed Zn atom model is performed based on the CASTEP module in Materials-Studio software under the first principles using GGA and PBE generalized function. The corresponding binding energies, bond lengths, bond angles, charge densities, energy band structures, densities of states, and optical properties were also analyzed. The Monkhorst-Pack particular K-point sampling method is used in the calculations; the K-point grid is 6 × 6 × 1, and the cutoff energy for the plane wave expansion is 500 eV. After geometric optimization, the iterative accuracy converges to a value of less than 1 × 10-5 eV/atom for the total energy of each atom and less than 0.03 eV/Å for all atomic forces. The thickness of the vacuum layer was set to 20 Å to avoid the effect of interlayer interaction forces. In this paper, 27 atoms were used to form a 3 × 3 × 1 supercellular tungsten disulfide system consisting of 18 S atoms and 9 W atoms.

Environmental health, economy, and amenities interactively drive migration patterns among China's older people.

The increasing number of older adult migrants is rapidly changing regional demographic and social structures in China. There is an urgent need to understand the spatial patterns and factors that influence older adults to migrate, especially the role of environmental health. However, this issue has been under-studied. This study focused on intra-provincial and inter-provincial older adult migrants as research subjects, estimated their spatial concentration index based on the iterative proportional fitting approach, and explored the factors influencing their migration using the GeoDetector Model. The results showed the following: (1) In 2015, more than 76% of inter-provincial older adult migrants were distributed in Eastern China, and most intra-provincial older adult migrants were scattered in sub-provincial cities. (2) Compared to factors relating to economy and amenities, environmental health by itself played a relatively weak role in the migration of older adults, but the interaction among environmental health, economy, and amenities was a key driving force of older adult migration. (3) There were significant differences in the dominant environmental health factors between inter-provincial migration and intra-provincial migration, which were temperature and altitude, respectively. Our findings can help policymakers focus on the composition of older adult migrants based on urban environmental health characteristics and rationally optimize older adult care facilities to promote supply-demand matching.

Effect of bending deformation on the electronic and optical properties of O atoms adsorbed by Be3N2.

CONTEXT: In this paper, the optimum coverage of 4.44% and the optimum adsorption sites were determined for the Be3N2 adsorption system of O atoms at different coverages based on density functional theory. The electronic and optical properties of the model were investigated by applying bending deformation to the model at these coverage and adsorption sites. Adsorption of O atoms disrupts the geometrical symmetry of Be3N2, resulting in orbital rehybridization and lowering its band gap. Bending deformation causes the band gap of the adsorbed O atom structure of Be3N2 to first increase and then decrease, resulting in the modulation of its band gap. With increasing bending deformation, the adsorbed system is redshifts, and the degree of redshift increases with increasing bending deformation. METHODS: All calculations in this paper were performed using the first-principles-based CASTEP module of Materials Studio (MS). The generalized gradient approximation (GGA) plane-wave pseudopotential method and the Perdew-Burke-Ernzerhof (PBE) Perdew et al. Phys Rev Lett 77:3865, 1996 generalized functional were used in the geometry optimization and calculation process to calculate the exchange-correlation potential between electrons. The effect of coverage on the electronic and optical properties of the Be3N2-adsorbed O atom system was investigated by adsorbing different numbers of O atoms on a monolayer of Be3N2. The Be3N2 protocell contains two N atoms and three Be atoms with a space community of P6/MMM (No.191). The original cell was expanded 3 times along the direction of the base vectors a and b in the Be3N2 plane to create a 3 × 3 × 1 monolayer Be3N2 supercell system. A vacuum layer of 15 Å is set in the direction of the crystal plane of the vertical monolayer Be3N2 supercell to eliminate interactions between adjacent layers. In the overall energy convergence test of the Be3N2 supercell, the plane wave truncation energy was set to 500 eV, and the energy difference between the calculations given in the literature Reyes-Serrato et al. J Phys Chem Solids 59:743-6, 1998 using 550 eV was less than 0.01 eV, verifying the reliability of the data at a truncation energy of 500 eV. The Monkhorst-Pack special k-point sampling method Monkhorst et al. Phys Rev B 13:5188, 1976 was used in the structural calculations, and the grid was set to 3 × 3 × 1. The geometric optimization parameters are set as follows: the self-consistent field iteration convergence criterion is 2.0 × 10-6 eV, and the iterative accuracy convergence value is not less than 1.0 × 10-5 eV/atom for the total force of each atom and less than 0.03 eV/Å for all atomic forces. In addition the high-symmetry k-point path is taken as Γ(0,0,0) → M(0,0.5,0) → K(- 1/3,2/3,0) → Γ(0,0,0) Chen et al, AIP Adv 8:105105, 2018.

First-principles study of the effect of S-atom doping on the optoelectronic properties of stanene.

CONTEXT: Based on the first principles, the influence of S-atom doping on the electronic and optical properties of stanene is comprehensively examined in this work. The results show that pure stanene is a quasi-metal with zero bandgap. After doping with an S atom, opening the bandgap of pure stanene becomes possible and the state of the stanene is converted from quasi-metal to semiconductor. Analysis of the density of states reveals that the density of states of all doped systems is primarily made of the p-orbital of the Sn. The overlap population analysis showed that charge transfer occurs between S and Sn atoms under different doping concentrations. The charge transfer increases with increasing doping concentration. The charge transfer reaches a maximum at a doping concentration of 9.38%. The increase in doping concentration causes blue-shifting of the absorption and reflection peaks of the doped system as compared to those of pure stanene. It is expected that these studies can provide theoretical guidance for the practical application of stanene in optoelectronic devices. METHODS: All simulations are undertaken with the Cambridge Sequential Total Energy Package (CASTEP) (Wei et al. Physica B: Condensed Matter 545:99, 2018; Bafekry et al. Phys Chem Chem Phys, 2021; Zala et al. Appl Surf Sci, 2022; Bafekry et al. Nanotechnology, 2021; Bafekry et al. Phys Chem Chem Phys, 2021; Bafekry et al. J Phys: Condens Matter, 2021), which is based on density functional theory (DFT). For the exchange correlation, the generalized gradient approximation (GGA) is implemented with the Perdew-Burke-Ernzerhof (PBE) functional Perdew et al. Phys Rev B Condens Matter 48:4978, 1993. Using the Monkhorst-Pack technique, a specific K-point sample of the Brillouin zone was carried out Monkhorst and Pack Phys Rev B 13:5188, 1976. After the convergence tests, the K-point grid was set to 3 × 3 × 1. The plane-wave truncation energy was set to 400 eV. The residual stress for all atoms was 0.03 eV/Å. The energy convergence criterion was 1.0 × 10-5 eV. To prevent recurring interactions between the layers, a vacuum layer with a thickness of 20 Å was established in the Z-direction.

Effect of compressive strain on electronic and optical properties of Cr-doped monolayer WS2.

CONTEXT: The electronic properties and optical properties of Cr-doped monolayer WS2 under uniaxial compressive deformation have been investigated based on density functional theory. In terms of electronic structure properties, both intrinsic and doped system bandgaps decrease with the increase of compression deformation, and the values of the bandgap under the same compression deformation after Cr doping are reduced compared with the corresponding intrinsic states. When the compressive deformation reaches 10%, both the intrinsic and doped system band gaps are close to zero. New electronic states and impurity energy levels appear in the WS2 system when doped with Cr atoms. For the optical properties, the calculation and analysis of the dielectric function under each deformation regime of monolayer WS2 show that the compression deformation affects the dielectric function, and when the compression deformation is 10%, the un-doped and Cr-doped regimes show a decrease in ε1(ω) compared to the compression deformation of 8%. For each deformation system, the peak reflections occur in the ultraviolet region. Near the position where the second peak of the absorption spectrum appears, it can be seen that the ability of each system to absorb light gradually decreases with the increase of the amount of deformation and appears to be red-shifted to varying degrees. METHODS: This study follows the initial principles of the density functional theory framework and is based on the CASTEP module of Materials-Studio software GGA and PBE generalizations are used to perform computations such as geometry optimization of the model. We have calculated the energy band structure of monolayer WS2 with intrinsic and compressive deformations of 2% and 4% using PBE and HSE06, respectively. The band gap values calculated using PBE are 1.802 eV, 1.663 eV, and 1.353 eV, respectively, and the band gap values calculated with HSE06 are 2.267 eV, 2.034 eV, 1.751 eV. The results show that the bandgap values calculated by HSE06 are significantly higher than those calculated by PBE, but the bandgap variations calculated by the two methods have the same trend, and the shape characteristics of the energy band structure are also the same. However, it is worth noting that the computation time required for the HSE06 calculation is much longer than that of the PBE, which is far beyond the capability of our computer hardware, and the purpose of this paper is to investigate the change rule of the effect of deformation on the bandgap value, so to save the computational resources, the next calculations are all calculated using the PBE. The Monkhorst-Pack special K-point sampling method is used in the calculations. The cutoff energy for the plane wave expansion is 400 eV, and the K-point grid is assumed to be 5 × 5 × 1. Following geometric optimization, the iterative precision converges to a value of less than 0.03 eV/Å for all atomic forces and at least 1 × 10-5 eV/atom for the total energy of each atom. The vacuum layer's thickness was selected at 20 Å to mitigate the impact of the interlayer contact force.

Bending deformation modulation of the optoelectronic properties of molybdenum ditelluride doped with nonmetallic atoms X (X = B, C, N, O): a first-principles study.

CONTEXT: A first-principles approach based on density functional theory was used to explore the effect of bending deformation on the electrical structure of molybdenum ditelluride doped with nonmetallic atoms X (X = B, C, N, and O). The study included alternate doping of nonmetallic atoms, as well as a comparison of the effects of intrinsic bending deformation and nonmetallic doping deformation. The results demonstrate that boron atom doping raises the Fermi energy level. Examining the energy band structure indicates that the intrinsic molybdenum ditelluride is a direct band gap semiconductor, which is transformed from a direct band gap to an indirect band gap after doping. We selected boron-doped systems for bending deformation and compared them with the intrinsic systems. With increasing deformation, all systems start to shift from semiconductor to metal. When the deformation reaches 8°, the energy levels fill and the electron energy increases. The intrinsically bent systems transition from direct band gap to indirect band gap and eventually to metal. The indirect band gap semiconductor-to-metal transition process occurs after the bending deformation of the boron-doped atoms. The analytical results show that the absorption and reflection peaks of the molybdenum ditelluride system are blue-shifted after the bending deformation of the boron-doped atoms. METHODS: Under fundamental principles, this research depends on the density functional theory framework (DFT) using the CASTEP module in the Materials-Studio software. The plane-wave pseudopotential approach with modified gradient approximation and the Perdew-Burke-Ernzerhof (PBE) generalized function is used for structure optimization and total energy calculations of the X-doped (X = B, C, N, O) MoTe2 system at different shape variables. Geometry optimization of the 27-atom superlattice MoTe2 was carried out, followed by alternative doping of tellurium atoms in the molybdenum ditelluride with B, C, N, and O. In this paper, the intrinsic bending deformation and B-doping of molybdenum ditelluride were selected for deformation analysis. Intrinsic bending deformations and boron-doped molybdenum ditelluride with bending angles ranging from 2° to 8° were employed for deformation investigation. In Fig. 1, pink is used to represent doped B atoms, orange is used to describe Te atoms, and green is used to represent Mo atoms. For the degree of deformation of molybdenum ditelluride, in this paper, it is expressed by the bending angle, i.e., the angle of the plane of molybdenum ditelluride after bending and deformation of a single layer of molybdenum ditelluride concerning the angle of the plane folded for the deformed plane. How to do it: For ease of presentation, the atomic chains are set to different colors. The purple part on both sides of the figure is bent and deformed, 3-5 atoms are fixed appropriately, and the middle part is deformed. On this basis, the bending deformation of intrinsically doped and boron-doped MoTe2 is comparatively analyzed. The effect of boron-doped atoms on the structure of MoTe2 is systematically investigated to study its structural stability and electronic structure. Fig. 1 a1 and a2 The main and side views of intrinsic MoTe2; b1 and (b2) the main and side views of MoTe2 doped with boron atoms bent by 8°.

First principle study of the effect of doping on the optoelectronic properties of Cr-adsorbed MoS2.

CONTEXT: This study explores, for the first time, using first principles, the impact of substitutional doping with boron (B), carbon (C), and nitrogen (N) on the adsorption of chromium (Cr) on monolayer MoS2. The effects of doping on the Cr adsorption behavior of MoS2 were investigated using four MoS2 systems, namely, pure, boron (B)-doped, carbon (C)-doped, and nitrogen (N)-doped, in order to gain an in-depth understanding of the mechanism of the effects of doping on the electronic structure and optical properties of Cr adsorbed by MoS2, to optimize the properties of MoS2, to explore new areas of application, and to promote the development of materials science. Four MoS2 adsorption systems of Cr adsorption on pure, B-doped, C-doped, and N-doped MoS2 were optimized, and the optimized results showed that the stable adsorption location of Cr on both pure and doped MoS2 was the hollow location at the top of the folded hexagon. The findings reveal that pure MoS2 has an adsorption effect on Cr, and doped elements B, C, and N can promote the adsorption of Cr on MoS2, and the strong and weak order of this promotion is B > C > N. METHODS: In this paper, we use the CASTEP module in the simulation software Materials Studio to perform simulation calculations and analyses to optimize the simulation of Cr adsorption by MoS2 doped with B, C, and N atoms using the generalized gradient approximation (GGA) plane-wave pseudo-potential method (Perdew et al. Phys Rev Lett 77(18):3865-3968, 1996), as well as Perdew-Burke-Ernzerhof (PBE) generalized functionals (Segall et al. J Phys: Condens Matter 14(11):2717-2744, 2022). The convergence test reveals that it is more reasonable to set the K-point network to 3 × 3 × 1 and the truncation energy to 400 eV. In this paper, a 3 × 3 × 1 supercell structure with 18 S atoms and 9 Mo atoms is selected. The convergence value of the iteration accuracy is 1.0e - 5eV/atom, and all the atomic forces are less than 0.02eV/Å. Additionally, to prevent MoS2 interlayer interaction, a vacuum layer with a thickness of 18 Å is set in the C direction. The geometrical optimization of the model is performed first, and then the corresponding adsorption energies of the model and the nature of the electronic structure are analyzed.

First-principles study of the effects of doping B, N, and O on the photoelectric properties of Cr adsorbed GaS.

CONTEXT: To lessen the impact of the dangerous metal Cr, this paper applies the first principles to investigate the adsorption behavior and photoelectric properties of GaS on Cr. The effects of doped GaS on Cr adsorption behavior are investigated with four GaS systems, which are pure, boron (B)-doped, nitrogen (N)-doped, and oxygen (O)-doped, in order to maximize the characteristics of GaS for use in novel sectors, to obtain understanding of the impact of doping on the electronic structure and optical properties of GaS adsorption of Cr, as well as to promote the development of the material. Four GaS adsorbed Cr systems, pure, B-doped, N-doped, and O-doped, are optimized, and the optimized results show that the stable adsorption position of Cr on both pure and doped GaS is the top position of Ga atoms, whereas doped elements B, N, and O can promote the adsorption of Cr on GaS, and the order of the strength of this promotion is B > N > O. METHOD: In this paper, molecular simulation calculations and analyses using the CASTEP module in the software Materials Studio are performed to simulate the structure optimization of GaS-adsorbed Cr materials doped with B, N, and O atoms by using the generalized gradient approximation (GGA) plane-wave pseudopotential approach [1] and the Perdew-Burke-Ernzerhof (PBE) generalized function [2]. From the convergence test, it is reasonable to set the K-point network to 4 × 4 × 1 and the truncation energy to 500 eV [3]. In this paper, a 3 × 3 × 1 supercell structure with 18 S atoms and 18 Ga atoms is selected. The convergence value of the iterative accuracy is 1.0e - 5 eV/atom, and all the atomic forces are less than 0.02 eV/Å. A vacuum layer of 16 Å is also set in the C direction to avoid interlayer interactions of GaS. First, we optimize the geometry of the model and then analyze the nature of the adsorption energy and electronic structure corresponding to the model.

Effect of tensile deformation on the optoelectronic properties of black phosphine-doped lithium atoms.

CONTEXT: First-principles calculations based on the generalized gradient approximation gradient and the Perdew-Burke-Ernzerhof function (GGA-PBE generalized function) are carried out on the intrinsic and lithium-doped black phosphine systems to investigate the effects of different uniaxial tensile deformations on the electronic and optical properties of the systems. It is shown that the structural stability of the intrinsic and lithium-doped systems decreases with increasing tensile deformation, and all systems are most stable at 0% tensile deformation. The intrinsic black phosphazene system is a direct band gap semiconductor, and its band gap increases and then decreases with tensile deformation and reaches a maximum value of 1.086 eV at 4%. Lithium doping closes the band gap of the black phosphazene system, which is metallic in nature, but the band gap is opened up when the tensile deformation is 4-6%. From the density of states analysis, the density of states of all systems is basically contributed by the s and p orbitals, with little contribution from the d orbitals, and the contribution from the p orbitals is dominant. From the analysis of optical properties, the increase of tensile deformation causes the absorption peaks of the intrinsic system to redshift then blueshift then redshift, causes the absorption peaks of the lithium-doped system to redshift, and causes the reflection peaks of all systems to redshift. In addition, lithium doping blueshifts the absorption and reflection peaks of the systems compared to the intrinsic black phosphazene system. METHODS: Using the CASTEP section of the Materials Studio software, first-principle calculations based on density functional theory are done on the top-site doped lithium atoms of monolayer black phosphine under uniaxial stretching deformation in the a-direction, and the generalized gradient approximation gradients and Perdew-Burke-Ernzerhof functions (GGA-PBE generalized functionals) are used for the optimization and approximation process. The optimization parameters are set for the supercell structure: its plane-wave truncation energy is set to 400 eV, its Brillouin zone K-point grid is set to 3*3*3, its self-consistent field iteration accuracy convergence value is 2.0e-6 eV/atom, the convergence basis of its structural optimization is 0.02 eV/ Å, and the convergence of the stress value is 0.05 gpa. During the optimization period, the interaction force between atoms is 0.03 eV/ Å and the atomic displacement is less than 0.001 Å. To eliminate the effect of interlayer forces, a vacuum layer with a thickness of 15 Å is placed in its vertical direction (i.e., c-axis direction).

Expression of Serum Anti-BP180/230 Antibodies in Bullous Pemphigoid Patients Combined with Nervous System Diseases and Relevant Factor Analysis.

OBJECTIVE: To explore the anti-BP230/180 and anti-BP180 antibodies in patients with bullous pemphigoid (BP) combined with neurological diseases, and to analyse the relevant factors. STUDY DESIGN: Analytical study. Place and Duration of the Study: Neurology Department, Cangzhou People's Hospital, Cangzhou, from April 2019 to June 2022. METHODOLOGY: Eighty BP patients were chosen based on associated neurological diseases, they were split into single (n=42) and combined groups (n=38). Expression of anti-BP180/230 antibodies was compared between the two groups. Associations with neurological diseases were analysed and the factors affecting the expression of anti-BP180/230 antibodies were explored. RESULTS: Out of 80 patients, 61 were positive for anti-BP180 antibodies and 58 were positive for anti-BP230 antibodies. The proportion of patients with positive anti-BP230/180 antibodies in the single group was considerably lower than in the combined group (p<0.05). Presence of both nervous system diseases and BP was found to be associated with the presence of anti-BP230/180 antibodies (p<0.001). Univariate analysis showed statistically significant association with age (<70 years, total IgE (>100 IU/ml), and EOS count >0.5 x 109/L (p<0.05). Logistic analysis demonstrated that age, total IgE and EOS count were independent risk factors affecting the expression of anti-BP180 and anti-BP23 antibodies (p<0.05). CONCLUSION: Serum anti-BP230/180 antibodies expression is abnormally high in BP patients having nervous system diseases. Combined nervous system diseases, age, total IgE and EOS count are independent risk factors affecting expression of anti-BP180/230 antibodies. KEY WORDS: Anti-BP180 antibody, Anti-BP230 antibody, Bullous pemphigoid, Nervous system diseases.

Effect of O-doping on electronic and optical properties of monolayer MoSe2 under shear deformation.

CONTEXT: In this study, the electronic structures and optical properties of the pure MoSe2 and O-doped MoSe2 systems under different shear deformations are calculated based on the first-principles approach. It is hoped to provide new possibilities for the design of novel controllable optoelectronic devices and to provide guidance for the application of MoSe2 in the field of optoelectronic devices. The findings indicate that both pure MoSe2 and O-doped MoSe2 systems are somewhat impacted by shear deformation. The pure MoSe2 undergoes a transition from direct to indirect and then to direct bandgap under shear deformation, but still maintains the semiconductor properties. The bandgap of the doped system changes from a direct to an indirect bandgap at 8% shear deformation. According to the examination of the density of states, we find that the density of states of the pure MoSe2 system is mainly contributed by the Mo-d and Se-p orbitals, and the total density of states of the system after O-atom doping mainly originates from the results of the contributions of the Mo-d, Se-p, and O-p orbitals. Optical property analysis reveals that the conductivity and peak value of the pure MoSe2 system are gradually red-shifted toward the low-energy region with the increase of shear deformation. The dielectric function of the O-doped MoSe2 system is red-shifted in the region of 6~10% shear deformation, and the degree of red-shift rises with deformation amount. The findings demonstrate that the electrical structure and optical characteristics of the O-doped MoSe2 system may be modulated effectively by shear deformation, providing a theoretical foundation for expanding the usage of MoSe2 materials in the field of optoelectronic devices. METHODS: This study is founded on the CASTEP module in the Materials-Studio software within the first-principles of the density-functional theory framework. The photoelectric properties of the intrinsic and doped systems under shear deformation are calculated using the Perdew-Burke-Ernzerh (PBE) of generalized function under the generalized gradient approximation (GGA). The Monkhorst-Pack special K-point sampling method is used in the calculations, and a 5 × 5 × 1 K-point grid is used for the calculations with a plane-wave truncation energy of 400 eV in the optimization of the structure of each model. After geometrical optimization, the energy convergence criterion for each atom is 1 × 10-5 eV/atom, the force convergence criterion is 0.05 eV/Å, and a vacuum layer of 20 Å in the c-direction is set.

First-principles study of the effect of doping on the optoelectronic properties of defective monolayers of MoSe2.

CONTEXT: In this paper, the structural stability, electronic structure, and optical properties of monolayer MoSe2 doped with C, O, Si, S, and Te atoms, respectively, under defective conditions are investigated based on first principles. It is found that the system is more structurally stable when defecting a single Se atom as compared to defecting a single Mo or two Se atoms. The electronic structure analysis of the system reveals that intrinsic MoSe2 is a direct bandgap semiconductor. The bandgap value of the system decreases with a single Se atom defect and introduces two new impurity energy levels in the conduction band. The defective systems doped with C and Si atoms all exhibit P-type doping. The total density of states of intrinsic MoSe2 is mainly contributed by the Mo-d and Se-p orbitals, and new density of state peaks appears near the conduction band after the defects of Se atoms. The total density of states of the defective system doped by each atom is mainly contributed by Mo-d, Se-p, and the result of the p orbital contribution of each dopant atom. By analyzing the dielectric function of each system, it is found that the intrinsic MoSe2 has the lowest static permittivity and the C-doped defect system has the highest static permittivity, which reaches 21.42. The C- and Si-doped defect systems are the first to start absorbing the light, and the intrinsic MoSe2 absorbs the light later, with its absorption edge starting at 1.25 eV. In the visible range, the reflection peaks of the systems move toward the high-energy region and the blue-shift phenomenon occurs. It is hoped that applying modification means to modulate the physical properties of the two-dimensional materials will provide some theoretical basis for broadening the application of monolayer MoSe2 in the field of optoelectronic devices. METHODS: This study utilizes the first principle computational software package MS8.0 (Materials studio8.0) under density functional theory (DFT). The exchange-correlation potential (GGA-PBE) is described by the Perdew-Burke-Ernzerhof correlation function in CASTEP, and the potential function adopts the ultrasoft pseudopotential in the inverse space formulation. The plane wave truncation energy Ecut is set to 400 eV, the K-point is taken as 5 × 5 × 1, and the force convergence criterion is 0.05 eV/Å. The convergence accuracy of the total energy of the system is less than 1.0 × 10-5 eV/atom, the tolerance shift is less than 0.002 Å, and the stress deviation is less than 0.1 GPa. The vacuum layer is taken as 15 Å, which is intended to minimize the interlayer force. The vacuum layer was set to 15 Å to avoid the effect of layer-to-layer interaction forces in the crystal cell.

First-principles study of the electronic structure and optical properties of C-doped SnS2.

CONTEXT: Density functional theory (DFT) was used to investigate the effects of varying carbon doping concentrations on the electronic and optical properties of SnS2-doped systems. The findings show that a doping concentration of 3.7% in SnS2 results in the highest structural stability and the lowest formation energy. A pure SnS2 monolayer is an indirect bandgap semiconductor, and the result reveals that increasing carbon doping correlates with a gradual reduction in the system's bandgap. The density of states analysis reveals that the valence band comprises C-2p, S-3p, and Sn-5p orbitals, whereas the conduction band consists of S-3p, Sn-5 s, and C-2p orbitals. Furthermore, doping concentration appears to cause a redshift in both the absorption coefficient and reflection peaks, which both decrease as doping concentration increases. METHODS: The calculations for this study were performed using DFT within the CASTEP module of Materials Studio Segall et al. J Phys: Condens Matter 14(11):2717, 2002. The system parameters and structures were optimized to determine the electronic structure and optical properties. Geometric optimization and calculations were carried out with the generalized gradient approximation plane-wave pseudopotential method and the Perdew-Burke-Ernzerhof functional Perdew et al. Phys Rev Lett 80(4):891-891, 1998. The parameters for structural optimization included a plane-wave expansion cutoff energy set at 500 eV and a k-point mesh of 6 × 6 × 1 for Brillouin zone integration. The electronic convergence criteria were established at 1.0 × 10-5 eV/atom for the unit cell energy and 1.0 × 10-6 eV/atom for self-consistency. The internal stress deviation was maintained below 0.05 GPa, the atomic force interactions were kept under 0.03 eV/Å, and atomic displacements during geometric optimization were confined to less than 0.001 Å. To calculate the properties of the SnS2 monolayer, a vacuum spacing of 15 Å along the z-axis was introduced to prevent interactions between adjacent layers.

Molecular dynamics study of the mechanical properties of hydrated calcium silicate enhanced by functionalized carbon nanotubes.

CONTEXT: The incorporation of functionalized carbon nanotubes can enhance the mechanical properties of cement-based materials. However, the types of functional groups and their roles in composite materials are not yet clear. In this study, molecular dynamics (MD) simulation methods were employed to investigate the mechanical performance of hybridized calcium silicate hydrate gel reinforced with pure carbon nanotubes, epoxy-coated carbon nanotubes, carboxylated carbon nanotubes, and hydroxylated carbon nanotubes. The results indicate that the addition of all four types of nanotubes can enhance the mechanical properties of hydrated calcium silicate gel compared to pure C-S-H. Tensile loading results show that carbon nanotubes can act as bridges for microcracks in the composite material, and functionalized nanotubes exhibit a better reinforcing effect than pure carbon nanotubes. Under tensile stress, hydroxylated nanotubes are more effective in increasing the toughness of the composite material, while carboxylated nanotubes tend to enhance the strength of the composite material. The compressive loading results indicate that the compressive strength of cement-based materials is higher than their tensile strength. Overall, carboxylated nanotubes show particularly remarkable performance in enhancing the mechanical properties of cement-based materials. Compared to pure C-S-H gel, the tensile and compressive elastic moduli of carboxylated nanotube/C-S-H composite material increased by 18.13% and 34.78%, respectively. Its tensile and compressive strengths also increased by 30.40% and 40.23%, respectively. METHOD: All molecular dynamics simulations were performed on the classical computational simulation platform LAMMPS. In this paper, the parameters in the ClayFF force field are chosen to simulate calcium hydrated silicate (/C-S-H), and the ClayFF-CVFF combined force field is used to simulate the mechanical properties of the CNT/C-S-H molecular model structure.

Effect of shear strain on the electronic and optical properties of Al-doped stanane.

CONTEXT: The quasi-metallic properties of stanene limit its prospects in optoelectronic devices. Based on first-principles calculations, a systematic study is conducted on the tuning effects of surface hydrogenation and Al atom doping on the electronic and optical properties of stanene. Surface hydrogenation serves as an ideal way to open the forbidden band of stanene, and Al atom doping further increases hydrogenated stanene (stanane) band gap to 0.460 eV. Deformation has a minor impact on the stability of the stanane-Al structure, while shear strain can effectively modulate the band gap engineering of the doped system, reducing the band gap value from 0.460 to 0.170 eV. Deformation induces a redshift in the absorption peak and reflectance, also slowing down the rate of decrease in the absorption coefficient, and enhancing the peak value of light reflectance, which is positively correlated with the degree of shear strain. These findings hold promise for expanding the potential application of monolayer stanane in semiconductor devices. METHODS: All calculations are performed using CASTEP module in Materials Studio based on the density functional theory (DFT). The Perdew-Burke-Ernzerhof (PBE) generalized gradient approximation (GGA) is employed to describe the exchange-correlation energy (Perdew et al., Phys Rev Lett 77(18), 1996). We construct models for both stanene and stanane. The original unit cell of stanene has two Sn atoms, while stanane consists of two Sn atoms and two H atoms, and expand them to a 3 × 3 × 1 supercell with a vacuum layer of 20 Å in height to prevent interlayer coupling. After convergence testing, the plane-wave cutoff energy is set to 450 eV, and the energy convergence threshold is set to 1 × 10-5 eV. The maximum residual stress for each atom is set to 0.01 eV/Å. Brillouin zone sampling is performed using a 6 × 6 × 1 k-point mesh based on the Monkhorst-Pack method (Monkhorst and Pack, Phys Rev B 13(12), 1976). The k-point accuracy of the density of states and optical properties is 9 × 9 × 1. All calculations are performed using the more advanced OTFG ultrasoft pseudopotential, and structural relaxations are performed using supercells to ensure that the model is fully relaxed. We use the HSE06 functional to calculate the energy band structures of stanane-Al deformed to 0%, 4%, and 8%, resulting in band gap values of 1.465 eV, 1.368 eV, and 1.016 eV, respectively. These values are significantly higher than those obtained using the PBE functional (0.460 eV, 0.397 eV, and 0.170 eV). However, the shapes and trends of the band structures obtained from both PBE and HSE06 calculations are similar. Additionally, the calculation time needed by HSE06 is greatly longer than PBE, which exceeds the capabilities of our computer hardware, and cannot support all subsequent calculations. To investigate the influence of deformations on the variation of band gap values and to conserve computational resources, the subsequent calculations in this study use the PBE functional.

First-principle study of shear deformation effect on Mg adsorption by monolayer SnS2.

CONTEXT: In this study, the effects of different shear deformations on the structural stability, electronic structure, and optical properties of a Mg atom adsorption system of S vacancy defect SnS2 are systematically investigated based on density functional theory. It is shown that the presence of an S-vacancy defect makes the band gap of the SnS2 system significantly smaller than that of the perfect SnS2 system, and the SnS2 system is changed from a direct band gap semiconductor to an indirect band gap semiconductor. The optimal adsorption position of a Mg atom on the S-vacancy SnS2 system is above the S atom where the adsorption energy is the largest and the system is the most stable. The density of states of the adsorption system is predominantly contributed by the S-3p and Sn-5 s orbital electrons. The imposition of shear deformation leads to the introduction of certain impurity energy levels in the adsorption system, and the forbidden bandwidth near the Fermi energy level decreases. As compared to the intrinsic SnS2, the absorption and reflection peaks of adsorption systems under different shear deformation are red-shifted and appear in the ultraviolet region. This improves the utilization of the adsorption system for ultraviolet light to a great extent. METHODS: The model calculations in this paper are performed using the CASTEP module of the Material Studio (MS) software based on the first principles of Density Functional Theory (DFT) (Wei et al. in Physica B 545:99-106, 2018) for plane wave artifacts. Geometrical optimization and computational procedures are used to calculate the exchange-correlation energy using the Perdew-Burke-Ernzerhof (PBE) generalized function (Perdew et al. in Phys Rev B Condens Matter 48:4978, 1993) of the generalized gradient approximation (GGA). The Monkhorst-Pack method (Monkhorst and Pack in Phys Rev B 13:5188-5192, 1976) was used to rationalize the sampling of the highly symmetric k-points in the Brillouin zone. The grid of k-points is set to be 6 × 6 × 1. The plane-wave truncation energy is set to be 400 eV. The energy convergence criterion is 1.0 × 10-5 eV. The residual stress of all atoms is 0.01 eV/Å. A vacuum layer with a thickness of 15 Å is set up in the z-direction, which ensures that the interactions of the system along the z-axis between the top and the bottom layers can be ignored during the whole simulation process. We construct a 3 × 3 × 1 SnS2 system containing 27 atoms as the computational model. The intrinsic SnS2 contains 9 Sn atoms and 18 S atoms.

Torsional deformation modulation of the electronic structure and optical properties of molybdenum ditelluride systems doped with halogen atoms X (X = F, Cl, Br, I): a first-principles study.

CONTEXT: Using a first-principles plane-wave pseudopotential technique within the context of density-functional theory, the electronic structure and optical properties of the molybdenum ditelluride system doped with halogen atoms X (X = F, Cl, Br, I) were investigated. The electronic structure, density of states, charge transfer, and optical properties of halogen atom X doped on MoTe2 monolayer are systematically calculated and analyzed. It shows that the Fermi energy level is shifted upward after doping with halogen atoms. With F-MoTe2 doping, the geometrical distortion is the most pronounced, the charge transfer number is the highest, and the semiconductor shifts from a direct band gap to an indirect band gap. When the torsional deformation is between 1° and 5°, the F-doped MoTe2 system stays an indirect band gap semiconductor and transitions to quasi-metal at 6°. It is shown that the torsional deformation can modulate the electronic properties of the doped structure and realize the semiconductor-metal transition. OPTICAL PROPERTIES: The F-doped system has a strong absorption peak reflection peak after torsion, and with the increase of torsion angle, the absorption peak is red-shifted, and the reflection peak is blue-shifted. Moreover, the absorption and reflection peaks start to decrease with the rise of the torsion angle. METHODS: We apply the generalized gradient approximation plane-wave pseudopotential technique based on Perdew-Burke-Ernzerhof (PBE) generalized functions, under the first principles of the density-functional theory framework. The overall optimization of the intrinsic molybdenum ditelluride structure and the halogen atom X-doped molybdenum ditelluride structure was carried out. Then, the F-doped molybdenum ditelluride system was selected for torsional deformation with torsion angles from 1° to 6° for computational analysis. SPECIFIC METHOD: To make the presentation more accessible, the atoms in the F-doped molybdenum ditelluride system were colored differently. The pink chain edge atoms were first reversed by θ°. Then, the blue chain edge atoms were reversed by θ° in the other direction. The middle row of atoms was adjusted accordingly to the different twisting angles of the two sides by doing the corresponding torsion with the torsion angle θ°/2 and fixing the individual atoms. The calculation employs the Monkhorst-Pack particular K-point sampling method. The 3 × 3 × 1 inverted-space K-point grid is utilized for material structure optimization calculations in each model, and the 9 × 9 × 1 K-point grid is used for material electronic structure calculations. A 15 Å vacuum layer is put on the crystal surface of vertical monolayer molybdenum ditelluride supercells to avoid interactions with adjoining cells.

First-principles study on the mechanical properties of cement mortar modified with functionalized graphene oxide.

CONTEXT: In this paper, first-principle calculations reveal that the shear strength of the graphene-cementitious interface (G/C-S-H) (12 MPa) is lower than that of the epoxy, hydroxyl and carboxyl graphene-cementitious interfaces (G-O/C-S-H, G-OH/C-S-H and G-COOH/C-S-H) (21 MPa, 29 MPa and 14 MPa). This indicates that the introduction of functional groups helps to improve the mechanical properties of the graphene-cementitious contact interface. Electrical analysis of the interface reveals that functional groups adsorbed on graphene change the electron distribution on the graphene surface. The formation of a contact interface between graphene and cementitious not only promotes the interaction between the two, but also serves as a bridge connecting the graphene and the cementitious, exacerbating the charge transfer between the two and promoting the generation of solid chemical bonds. METHOD: All calculations were performed by the CASTEP module in Materials Studio software, using the GGA-PBE functional for structural optimization. The convergence criteria for the geometry optimization are set to a self-consistent field iteration convergence criterion of 2.0 × 10-6 eV and a structural optimization convergence criterion of 0.02 eV/Å.

Effect of strain on the electronic structure and optical properties of Cr-doped monolayer MoS2.

CONTEXT: In this paper, the electronic and optical properties of Cr-doped monolayer MoS2 under uniaxial tensile strain are investigated by first-principle calculations. It is shown that uniaxial tensile strain can significantly change the electronic and optical properties of Cr-doped monolayer MoS2, and the bandgap value of the intrinsic MoS2 system gradually decreases with the increase of tensile strain, while the bandgap value of the Cr-doped MoS2 system is relatively stable. However, when the stretching reaches a certain degree, both the intrinsic and doped systems become metallic. From the analysis of the density of states, it is found that new electronic states and energy levels appear in the intrinsic MoS2 system and all Cr-doped monolayer MoS2 systems with the increase of the tensile strain, but the changes in the density of states diagrams of the Cr-doped monolayer MoS2 system are relatively small, which is mainly attributed to the effect of the Cr-doped atoms. The analysis of optical properties displays that the stretched doped system differs from the intrinsic MoS2 system in terms of dielectric function, absorption and reflection, energy loss function, and refractive index. Our results suggest that uniaxial tensile strain can be used as an effective means to modulate the electronic structure and optical properties of Cr-doped monolayer MoS2. These findings provide a theoretical basis for understanding the optoelectronic properties of MoS2 and its doped systems as well as their applications in optoelectronic devices. METHODS: Based on the first principle of density functional theory framework and the CASTEP module in Materials Studio software (Perdew et al. in Phys Rev Lett 77(18):3865-3868, 1996). The structure of Cr atom-doped MoS2 systems and MoS2 systems were optimized using the generalized gradient approximation plane-wave pseudopotential method (GGA) and Perdew-Burke-Ernzerhof (PBE) generalized functions under 3%, 6%, and 9% tensile deformation, and the corresponding formation energy, bond length, electronic structure, and optical properties of the models were analyzed. The Grimme (J Comput Chem 27(15):1787-1799, 2006) vdW correction with 400 eV cutoff was used in Perdew-Burke-Ernzerhof (PBE) functional to optimize the geometry until the forces and energy converged to 0.02 eV/Å and 1.0e-5eV/atom, respectively. For each model structure optimization, the K-point grid was assumed to be 4×4×1, using the Monkhorst-Pack special K-point sampling method. After the MoS2 supercell convergence test, the plane-wave truncation energy was chosen to be 400 eV. Following geometric optimization, the iterative accuracy converged to no less than 1.0×10-5 eV/atom for total atomic energy and less than 0.02 eV/Å for all atomic forces. We created a vacuum layer of 18 Å along the Z-axis to prevent the impact of periodic boundary conditions and weak van der Waals forces between layers on the monolayer MoS2. In this paper, a total of 27 atoms were used for the 3×3×1 supercell MoS2 system, which consists of 18 S atoms and 9 Mo atoms.