Computational Insight into the Physical Properties of Bulk MP (M = Li, Na, K) for Energy Applications.

In this study, we applied density functional theory to compute the electronic, optical, and thermal properties of MP (M = Li, Na, K). We find that the materials under consideration are stable, owing to the lack of negative frequencies in the phonon spectra. LiP exhibits an indirect band gap of 1.43 eV. NaP and KP have direct band gaps of 1.67 and 1.76 eV, respectively. The family of these composites shows strong absorption, observed by their very sharp absorption edges and confirmed by their direct transition from the valence to conduction band. They exhibit strong absorption below 4.0 eV in the optical spectra, which could serve in a solar cell device. The thermal calculations show high zT values of 0.74, 0.78, and 0.64 at 300 K for LiP, NaP, and KP, respectively. Thus, our results could be promising for electronic and thermal devices.

Study of the Influence of Electron Spin in Ferromagnetism and Thermoelectric Characteristics of CdTm2Y4 (Y = S, Se) Spinels for Spintronic Applications.

The current study used full-potential methods to examine the ferromagnetic characteristics of CdTm2Y4(Y= S, Se) spinels; i.e., structural, elastic, electronic, and thermoelectric characteristics of these spinels have been explored for the first time. We used PBEsol-GGA for enthalpy of formation calculations to explain the stability of the ferromagnetic state and calculate the elastic constants and corresponding mechanical modules to reveal the ductile behavior of the materials. The mBJ potential is used instead of PBEsol-GGA to obtain more accurate and precise results of electronic and thermoelectric characteristics. Using mBJ potential leads to complete occupation of the bands in the materials and a clear interpretation of the density of states (DOS). The analysis of the electronic band structure and DOS reveals the stability of the ferromagnetic state in the analyzed materials as a result of p-d hybridization-based exchange splitting of Tm cations in the lattice. The calculations of thermoelectric efficiency are effective in evaluating the aptitude pertinence of the material in waste energy recovery systems and other technological applications. The thermal parameters of these materials are also analyzed to examine their thermal stability over a wide range of temperatures. The results of these calculations are essential for determining the suitability of the materials for use in spintronics-based devices and thermoelectric appliances as these devices rely heavily on the material's thermoelectric properties.

Materials and interfaces properties optimization for high-efficient and more stable RbGeI3 perovskite solar cells: optoelectrical modelling.

In this research work, we investigated the effects of a broad set of materials properties and external operating parameters on the opto-electrical output of a hybrid RbGeI3-based perovskite solar cell (PSC) as a means of enhancing its performance. We first performed a judicious numerical modelling of the reference cell with the following structure FTO/TiO2/RbGeI3/Spiro-OMeTAD/Ag, with data retrieved from the experiment. SCAPS program enables to model the device, considering charge carriers transport governing equations. Investigations are directed on addressing the current challenges that include thinner, less environmentally harmful, cost-effectiveness, and more stable solar devices over time. Analysis of the effects of different hole transport material (HTM) on current-voltage (J-V) and external quantum efficiency (QE) characteristics, helps to identify CuI as an ideal HTM. Optimal cell output were achieved by investigating the effects of metal contact work function, defect states, RbGeI3 thickness, light transmission/reflection at the front/back contact, as well as operating temperature. As a result, efficiency increased significantly from 10.11 to 18.10%, and fill factor that represents a stability indicator, increased from 63.68 to 76.95%. Moreover, an optimum open-circuit voltage Voc = 0.70 V and a high short-circuit current density of Jsc = 33.51 mA/cm2 were recorded. An additional study on the capture cross-section of charge carriers ([Formula: see text]) on PV characteristics, enabled to achieve a power conversion efficiency (PCE) of 29.71% and FF of 88% at a value of [Formula: see text] selected to be 10-22 cm2. This contribution aims at designing and producing thinner, more efficient, more stable and more environmentally clean and economically viable PSCs.

A Thorough Investigation of Electronic, Optical, Mechanical, and Thermodynamic Properties of Stable Glasslike Sodium Germanate under Compressive Hydrostatic Pressure: Ab Initio Study.

In this paper, we have tried to elucidate the variation of structural, electronic, and thermodynamic properties of glasslike Na2GeO3 under compressive isotropic pressure within a framework of density functional theory (DFT). The result shows stable structural (orthorhombic → tetragonal) and electronic (indirect → direct) phase transitions at P ∼ 20 GPa. The electronic band gap transition plays a key role in the enhancement of optical properties. The results of the thermodynamic properties have shown that Na2GeO3 follows Debye's low-temperature specific heat law and the classical thermodynamic of the Dulong-Petit law at high temperature. The pressure sensitivity of the electronic properties led us to compute the piezoelectric tensor (both in relaxed and clamped ions). We have observed significant electric responses in the form of a piezoelectric coefficient under applied pressure. This property suggested that Na2GeO3 could be a potential material for energy harvest in future energy-efficient devices. As expected, Na2GeO3 becomes harder and harder under compressive pressure up to the phase transition pressure (∼20 GPa) which can be read from Pugh's ratio (kH) > 1.75, however, at pressures above 20 GPa kH < 1.75, which may be due to the formation of fractures at high pressure.

Adsorption of NO x (x = 1, 2) Molecules on the CoFeMnSi(001) Surface: First-Principles Insights.

In this article, the adsorption of NO x (x = 1, 2) gas molecules on the (001) surface of CoFeMnSi quaternary Heusler alloys has been investigated theoretically with density functional theory (DFT) calculations. The adsorption strength was estimated with adsorption energy (E a), magnitude of charge transfer (ΔQ), charge density difference (CDD), minimum distance between molecule and surface (d), and adsorption mechanism was analyzed with density of states. The results showed that unlike half-metallic nature of the bulk phase, the pristine CoFeMnSi(001) surface exhibited metallic character caused by the emergence of electronic states of the atoms in the top-most layer of the surface. It was found that both NO and NO2 molecules undergo chemical adsorption and strongly interact with the surface evidenced by the large value of E a and ΔQ. In particular, the NO x molecule dissociates into N and O atoms for some adsorption configurations. Bader charge analysis reveals that NO x molecules act as charge acceptors by drawing charge from the surface atoms through p-d hybridization. Such findings might be useful in the development of Heusler alloys based gas sensors.

Synergy of Small Antiviral Molecules on a Black-Phosphorus Nanocarrier: Machine Learning and Quantum Chemical Simulation Insights.

Favipiravir (FP) and Ebselen (EB) belong to a broad range of antiviral drugs that have shown active potential as medications against many viruses. Employing molecular dynamics simulations and machine learning (ML) combined with van der Waals density functional theory, we have uncovered the binding characteristics of these two antiviral drugs on a phosphorene nanocarrier. Herein, by using four different machine learning models (i.e., Bagged Trees, Gaussian Process Regression (GPR), Support Vector Regression (SVR), and Regression Trees (RT)), the Hamiltonian and the interaction energy of antiviral molecules in a phosphorene monolayer are trained in an appropriate way. However, training efficient and accurate models for approximating the density functional theory (DFT) is the final step in using ML to aid in the design of new drugs. To improve the prediction accuracy, the Bayesian optimization approach has been employed to optimize the GPR, SVR, RT, and BT models. Results revealed that the GPR model obtained superior prediction performance with an R2 of 0.9649, indicating that it can explain 96.49% of the data's variability. Then, by means of DFT calculations, we examine the interaction characteristics and thermodynamic properties in a vacuum and a continuum solvent interface. These results illustrate that the hybrid drug is an enabled, functionalized 2D complex with vigorous thermostability. The change in Gibbs free energy at different surface charges and temperatures implies that the FP and EB molecules are allowed to adsorb from the gas phase onto the 2D monolayer at different pH conditions and high temperatures. The results reveal a valuable antiviral drug therapy loaded by 2D biomaterials that may possibly open a new way of auto-treating different diseases, such as SARS-CoV, in primary terms.

Engineering of Hydrogenated (6,0) Single-Walled Carbon Nanotube under Applied Uniaxial Stress: A DFT-1/2 and Molecular Dynamics Study.

Herein, we systematically studied the electronic, optical, and mechanical properties of a hydrogenated (6,0) single-walled carbon nanotube [(6,0) h-SWCNT] under applied uniaxial stress from first-principles density functional theory (DFT) and molecular dynamics (MD) simulation. We have applied the uniaxial stress range from -18 to 22 GPa on the (6,0) h-SWCNT (- sign indicates compressive and + indicates tensile stress) along the tube axes. Our system was found to be an indirect semiconductor (Γ-Δ), with a band gap value of ∼0.77 eV within the linear combination of atomic orbitals (LCAO) method using a GGA-1/2 exchange-correlation approximation. The band gap for (6,0) h-SWCNT significantly varies with the application of stress. The indirect to direct band gap transition was observed under compressive stress (-14 GPa). The strained (6,0) h-SWCNT showed a strong optical absorption in the infrared region. Application of external stress enhanced the optically active region from infrared to Vis with maximum intensity within the Vis-IR region, making it a promising candidate for optoelectronic devices. Ab initio molecular dynamics (AIMD) simulation has been used to study the elastic properties of the (6,0) h-SWCNT which has a strong influence under applied stress.

Lowering Cost Approach for CIGS-Based Solar Cell Through Optimizing Band Gap Profile and Doping of Stacked Active Layers-SCAPS Modeling.

In this research article, we carry out investigation on compensating the efficiency loss in thin-film CIGS photovoltaic (PV) cell due to absorber coat depth reduction. We demonstrate that the efficiency loss is mainly caused by the disruption of the charge-carrier transport. We propose an architecture engineered with a stepped band gap profile for improving the efficiency of charge-carrier transport and collection. By modifying the gallium content, we tuned the band gap profile of the active layer of a reference experimental cell from which we previously collected all parameters. Using the simulator environment SCAPS-1D, we modeled a three-steps stacking profile of active layer with different gallium contents from one layer to another. Based on the results obtained, the band gap configuration herein proposed appears to be a prospective strategy for high-performance ultrathin Cu(In,Ga)Se2-based PV cell architecture engineering. By combining this approach with the optimization of the active layer doping, we enhanced the yields of the reference structure from 18.93% for a 2 µm active layer to 23.36% for only 0.5 µm thickness of active layer, that is, an enhancement of 4.4%. The fill factor increased from 73.24 to 81.73%, that is, an additional stability indicator value of 8.5%. The good values of the obtained efficiency and the improvement of the fill factor value are relevant indicators of a stable device. Active layer stacking combined with a stepped band gap profile and doping level optimization is definitely providing new perspectives in thin-film CIGS high-performance PV cell achievement.

Electronic, magnetic, optical and thermoelectric properties of co-doped Sn1-2x Mn x A x O2 (A = Mo, Tc): a first principles insight.

The electronic, magnetic, optical and thermoelectric (TE) properties of Sn1-2x Mn x A x O2 (A = Mo/Tc) have been examined using density functional theory (DFT) based on the FP-LAPW approach. The results suggested that all the doped compounds show a half-metallic ferromagnet property with a 100% spin polarization at the Fermi level within GGA and mBJ. Moreover, doping SnO2 with double impurities reduces the bandgap. The reduced bandgaps are the result of impurity states which arise due to the Mn and Mo/Tc doping, leading to the shifts of the minima of the conduction band towards the Fermi energy caused by substantial hybridization between transition metals 3d-4d and O-2p states. Also, the (Mn, Mo) co-doped SnO2 system exhibits a ferromagnetic ground state which may be explained by the Zener double exchange mechanism. While the mechanism that controls the ferromagnetism in the (Mn, Tc) co-doped SnO2 system is p-d hybridization. Therefore, the role of this study is to illustrate the fact that half-metallic ferromagnet material is a good absorber of sunlight (visible range) and couples to give a combined effect of spintronics with optronics. Our analysis shows that Sn1-2x Mn x Mo x O2 and Sn1-2x Mn x Tc x O2 are more capable of absorbing sunlight in the visible range compared to pristine SnO2. In addition, we report a significant result for the thermoelectric efficiency ZT of ∼0.114 and ∼0.11 for Sn1-2x Mn x Mo x O2 and Sn1-2x Mn x Tc x O2, respectively. Thus, the coupling of these magnetic, optical, and thermoelectric properties in (Mn, A = Mo or Tc) co-doped SnO2 can predict that these materials are suitable for optoelectronic and thermoelectric systems.

Storage of Na in 2D SnS for Na ion batteries: a DFT prediction.

The high demand for renewable and clean energy has driven the exploration of advanced energy storage systems. Sodium-ion batteries (SIBs) are considered to be potential substitutes for Li-ion batteries (LIBs) because they are manufactured from raw materials that are cheap, less toxic, and abundantly available. Recent developments have demonstrated that two-dimensional (2D) materials have gained increasing interest as electrode candidates for efficient SIBs because of their enormous surface area and sufficient accommodating sites for the storage of Na ions. Herein, we explore the binding and diffusion mechanisms of Na on a 2D SnS sheet using density functional theory (DFT). The outcomes reveal that Na has a strong binding strength with SnS as well as charge transfer from Na to SnS, which affirms an excellent electrochemical performance. A transition from semiconducting (1.4 eV band gap) to metallic has been noted in the electronic structure after loading a minor amount of Na. In addition, a low open-circuit voltage (OCV) of 0.87 V and a high storage capacity of 357 mA h g-1 show the suitability of the SnS monolayer for SIBs. In addition, the low activation barrier for Na migration (0.13 eV) is attractive for a fast sodiation/desodiation process. Henceforth, these encouraging outcomes suggest the application of the SnS sheet as an excellent anode for next-generation SIBs.

Numerical Simulation of the Performance of Sb2Se3 Solar Cell via Optimizing the Optoelectronic Properties Based SCAPS-1D.

Antimony trisulfide (Sb2Se3), a non-toxic and accessible substance, has possibilities as a material for use in solar cells. The current study numerically analyses Sb2Se3 solar cells through the program Solar Cell Capacitance Simulator (SCAPS). A detailed simulation and analysis of the influence of the Sb2Se3 layer's thickness, defect density, band gap, energy level, and carrier concentration on the devices' performance are carried out. The results indicate that a good device performance is guaranteed with the following values in the Sb2Se3 layer: an 800 optimal thickness for the Sb2Se3 absorber; less than 1015 cm-3 for the absorber defect density; a 1.2 eV optimum band gap; a 0.1 eV energy level (above the valence band); and a 1014 cm-3 carrier concentration. The highest efficiency of 30% can be attained following optimization of diverse parameters. The simulation outcomes offer beneficial insights and directions for designing and engineering Sb2Se3 solar cells.

Vanadium Carbide (V4C3) MXene as an Efficient Anode for Li-Ion and Na-Ion Batteries.

Li-ion batteries (LIBs) and Na-ion batteries (SIBs) are deemed green and efficient electrochemical energy storage and generation devices; meanwhile, acquiring a competent anode remains a serious challenge. Herein, the density-functional theory (DFT) was employed to investigate the performance of V4C3 MXene as an anode for LIBs and SIBs. The results predict the outstanding electrical conductivity when Li/Na is loaded on V4C3. Both Li2xV4C3 and Na2xV4C3 (x = 0.125, 0.5, 1, 1.5, and 2) showed expected low-average open-circuit voltages of 0.38 V and 0.14 V, respectively, along with a good Li/Na storage capacity of (223 mAhg-1) and a good cycling performance. Furthermore, there was a low diffusion barrier of 0.048 eV for Li0.0625V4C3 and 0.023 eV for Na0.0625V4C3, implying the prompt intercalation/extraction of Li/Na. Based on the findings of the current study, V4C3-based materials may be utilized as an anode for Li/Na-ion batteries in future applications.

Pressure-Induced Enhanced Optical Absorption in Sulvanite Compound Cu3TaX4 (X = S, Se, and Te): An ab Initio Study.

Ab initio study on the family of ternary copper chalcogenides Cu3TaX4 (X = S, Se, and Te) is performed to investigate the suitability of these compounds to applications as photovoltaic absorber materials. The density functional theory based full potential linearized augmented plane wave method (FP-LAPW method) is employed for computational purposes. The electronic structure and optical properties are determined including electron-electron interaction and spin-orbit coupling (SOC), within the generalized gradient approximation plus Hubbard U (GGA+U) and GGA+U+SOC approximation. The large optical band gaps of Cu3TaS4 and Cu3TaSe4 considered ineffective for absorber materials, and also the hole effective mass has been modulated through applied pressure. These materials show extreme resistance to external pressure, and are found to be stable up to a pressure range of 10 GPa, investigated using phonon dispersion calculations. The observed optical properties and the absorption coefficients within the visible-light spectrum make these compounds promising materials for photovoltaic applications. The calculated energy and optical band gaps are consistent with the available literature and are compared with the experimental results where available.

Adsorption of CO over the Heusler alloy CrCoIrGa(001) surface: first-principles insights.

In this study, the adsorption of CO molecule over (001) surface of the Heusler alloy CrCoIrGa, has been investigated using DFT+U calculations. It is demonstrated that, after relaxation, the (001) surface retains the bulk atomic positions, exhibiting no apparent surface reconstruction. Owing to the emergence of unsaturated bonds at the surface, the surface layer atoms are found to carry more spin-polarization (SP) and atomic moments than that of inner layer atoms. The ground state total SP (magnetic moment) is found to be 27% (42.256 µ B). To explore the CO adsorption over the surface, five different adsorption configurations (sites) are considered and the strength of CO to surface interaction is estimated from the computed density of states (DOS), adsorption energy (E a), change in magnetic moment (ΔM), vertical height between molecule and surface (h), charge transfer (ΔQ), and charge density difference (CDD) plots. For all configurations, the E a lies in the range of -2.15 to -2.34 eV, with CO molecule adsorbed on the top of Ir atom as the most favorable adsorption configuration. The observed E a, ΔQ, h, and ΔM values, collectively predict that the (001) surface has strong interaction (chemisorption) with CO gas molecule, thus, might be useful in gas sensing applications.

Enhanced H2 Storage Capacity of Bilayer Hexagonal Boron Nitride (h-BN) Incorporating van der Waals Interaction under an Applied External Electric Field.

Lightweight two-dimensional materials are being studied for hydrogen storage applications due to their large surface area. The characteristics of hydrogen adsorption on the h-BN bilayer under the applied electric field were investigated. The overall storage capacity of the bilayer is 6.7 wt % from our theoretical calculation with E ads of 0.223 eV/H2. The desorption temperature to remove the adsorbed H2 molecules from the surface of the h-BN bilayer system in the absence of an external electric field is found to be ∼176 K. With the introduction of an external electric field, the E ads lies in the range of 0.223-0.846 eV/H2 and the desorption temperature is from 176 to 668 K. Our results show that the external electric field enhances the average adsorption energy as well as the desorption temperature and thus makes the h-BN bilayer a promising candidate for hydrogen storage.

Correction: A first-principles study of the stability, electronic structure, and optical properties of halide double perovskite Rb2Sn1-xTexI6 for solar cell applications.

Correction for 'A first-principles study of the stability, electronic structure, and optical properties of halide double perovskite Rb2Sn1-xTexI6 for solar cell applications' by Muhammad Faizan et al., Phys. Chem. Chem. Phys., 2021, 23, 4646-4657, DOI: 10.1039/D0CP05827K.

A first-principles study of the stability, electronic structure, and optical properties of halide double perovskite Rb2Sn1-xTexI6 for solar cell applications.

Owing to their emerging role in solar cell technology, lead halide perovskites have aroused significant research interest in the recent past. However, due to its obvious toxicity, looking for a potential alternative to lead is becoming one of the most important pursuits in present times. We present our work based on density functional theory (DFT) investigating lead free defect perovskites (Rb2Sn1-xTexI6 (0 ≤x≤ 1)). In particular, we explore the crystal structure, thermodynamic stability, electronic structure, and optical properties of Rb2Sn1-xTexI6 (0 ≤x≤ 1) as a function of increasing Te concentration. Our results show that the Sn-Te alloyed perovskites exhibit considerable stability, a suitable band gap, small effective mass, and excellent light absorption. Especially, Rb2Sn0.75Te0.25I6 and Rb2Sn0.50Te0.50I6 have a direct band gap of 1.35 and 1.44 eV, respectively, which is highly favorable for use in a single-junction photovoltaic cell. We hope that our work will arouse the interest of experimental as well as theoretical scientists for synthesizing new materials and/or exploring the Sn-Te mix as a potential substitute for lead in photovoltaic materials.

Compositional Engineering Study of Lead-Free Hybrid Perovskites for Solar Cell Applications.

Hybrid organic-inorganic perovskite solar cells (HOIPs), especially CH3NH3PbI3 (MAPbI3), have received tremendous attention due to their excellent power conversion efficiency (25.2%). However, two fundamental hurdles, long-term stability and lead (Pb) toxicity, prevent HOIPs from practical applications in the solar industry. To overcome these issues, compositional engineering has been used to modify cations at A- and B-sites and anions at the X-site in the general form ABX3. In this work, we used the density functional theory (DFT) to incorporate Rb, Cs, and FA at the A-site to minimize the volatile nature of MA, while the highly stable Ca2+ and Sr2+ were mixed with the less stable Ge2+ and Sn2+ at the B-site to obtain a Pb-free perovskite. To further enhance the stability, we mixed the X-site anions (I/Br). Through this approach, we introduced 20 new perovskite species to the lead-free perovskite family and 7 to the lead-containing perovskite family. The molecular dynamic (MD) simulations, enthalpy formation, and tolerance and octahedral factor study confirm that all of the perovskite alloys we introduced here are as stable as pristine MAPbI3. All Pb-free perovskites have suitable and direct band gaps (1.42-1.77 eV) at the Γ-point, which are highly desirable for solar cell applications. Most of our Pb-free perovskites have smaller effective masses and exciton binding energies. Finally, we show that the introduced perovskites have high absorption coefficients (105 cm-1) and strong absorption efficiencies (above 90%) in a wide spectral range (300-1200 nm), reinforcing their significant potential applications. This study provides a new way of searching for stable lead-free perovskites for sustainable and green energy applications.

Electronic properties and low lattice thermal conductivity (κ l) of mono-layer (ML) MoS2: FP-LAPW incorporated with spin-orbit coupling (SOC).

This paper focuses on the electronic and thermoelectric properties of monolayer MoS2. Here, we have examined the structure of MoS2, in which the hole in the center of the hexagonal cage is considered as a void atom, termed 1H-MoS2. Density functional theory (DFT) employing the generalized gradient approximation (GGA) and spin-orbit coupling (SOC) has been used for all calculations. Incorporation of SOC resulted in a significant change in the profile of the band energy, specifically the splitting of the valence band maximum (VBM) into two sub-bands. The "split-off" energy is found to be ∼20.6 meV. The reduction of the band gap with SOC is a prominent feature at the K-K location in the Brillouin zone. The band gap calculated with the GGA is ∼1.75 eV. However, on implementation of SOC, the GGA band gap was reduced to ∼1.68 eV. The frequency-dependent phonon dispersion curve was obtained to analyse the thermodynamical stability. 1H-MoS2 is found to be thermodynamically stable with no imaginary frequency. We report a low value of lattice thermal conductivity (κ l) and low electron effective masses, which are desirable for potential applications in thermoelectric devices.

Emergent electronically-controllable local-field-inducer based on a molecular break-junction with magnetic radical.

Molecular spintronics devices are receiving extensive research attention, due to their potential applications as the smallest memory and logic elements. A most fundamental issue in this field lies in generating spin polarized currents. In this communication, with the aid of the celebrated Wilson's numerical renormalization group (NRG) method, we propose theoretically a novel strategy to induce a local magnetic field that only affects the strongly correlated molecule under consideration, and could easily be manipulated through purely electronic technologies. It is also demonstrated that the device may lead to bidirectional spin polarization, where perfectly polarized spin-up and -down currents could be obtained by simply adjusting the energy level of the molecule to different regions along a single direction. Our suggested model is based on a molecular break-junction with a magnetic radical. It may provide a prospective example of a magnetoelectronics device at the molecular scale, which works without an external magnetic field.