Density functional theory study of the electronic and optical properties of pentagraphyne nanotubes.

Pentagraphyne (PG-yne), a recently predicted two-dimensional (2D) carbon allotrope with appealing properties, has opened up possibilities for a wide range of applications. In this study, we investigate the structural, electronic, optical, and electrical transport properties of a novel one-dimensional (1D) system called pentagraphyne nanotubes (PG-yneNTs), formed by rolling a PG-yne sheet, using density functional theory (DFT) calculations. We design PG-yneNTs with diameters ranging from 6.94 Å to 13.62 Å and employ state-of-the-art theoretical calculations to confirm their energetic, dynamic, and thermodynamic stability. Our electronic band structure calculations reveal that all these nanotubes are wide indirect band gap semiconductors. Remarkably, PG-yneNTs exhibit superior optical properties, including high absorption coefficients and absorption spectra covering the visible regime of the electromagnetic spectrum, making them potential candidates for visible-light-driven photocatalysis and solar cells. Interestingly, both the electronic and optical band gaps increase with the diameter of the nanotubes. Additionally, the observation of negative differential resistance (NDR) phenomena in (4, 0) PG-yneNT suggests their potential applications in NDR devices such as fast switches, frequency multipliers, and memory devices.

Bandgap prediction of non-metallic crystals through machine learning approach.

The determination of bandgap is the heart of electronic structure of any material and is a crucial factor for thermoelectric performance of it. Due to large amount to data (features) that are related to bandgap are now a days available, it is possible to make use of machine learning (ML) approach to predict the bandgap of the material. The study commences by selecting the feature through Pearson correlation study between bandgap and various thermoelectric parameters in non-metallic crystals. Among the 42 parameters available in the dataset, the Seebeck coefficient and its corresponding temperatures show high correlation with the bandgap. With these three selected features we have used different ML models like multilinear regression, polynomial regression, random forest regression and support vector regression to predict the bandgap. Amongst the different ML models considered, random forest regression outperforms the other models to predict the bandgap withR2value of 97.55% between actual bandgap and predicted bandgap.

Ink Drop Displacement Model-Based Direct Binary Search.

A novel statistical ink drop displacement (IDD) printer model for the direct binary search (DBS) halftoning algorithm is proposed. It is intended primarily for pagewide inkjet printers that exhibit dot displacement errors. The tabular approach in the literature predicts the gray value of a printed pixel based on the halftone pattern in some neighborhood of that pixel. However, memory retrieval time and the complexity of memory requirements hamper its feasibility in printers that have a very large number of nozzles and produce ink drops that affect a large neighborhood. To avoid this problem, our IDD model embodies dot displacements by moving each perceived ink drop in the image from its nominal location to its actual location, rather than manipulating the average gray values. This enables DBS to directly compute the appearance of the final printout without retrieving values from a table. In so doing, the memory issue is eliminated and the computation efficiency is enhanced. The deterministic cost function of DBS is replaced by the expectation over the ensemble of the displacements for the proposed model such that the statistical behavior of the ink drops is accounted for. Experimental results show significant improvement in the quality of the printed image over the original DBS. Besides, the image quality obtained by the proposed approach appears to be slightly better than that obtained by the tabular approach.

Highly Selective Ethyl Mercaptan Sensing Using a MoSe2/SnO2 Composite at Room Temperature.

Volatile organic sulfur compounds (VOSCs) serve not only as biomarkers for dental diseases such as halitosis but also as a tracer for monitoring air quality. Room-temperature selective detection and superior sensitivity against VOSCs at a sub-ppm level has remained a challenging task. Here, we propose a heterostructure-based design using a MoSe2/SnO2 composite for achieving sensitive and selective detection of ethyl mercaptan at room temperature. The composite was synthesized via a facile two-step method. A composite-based device has shown detection down to 1 ppm of ethyl mercaptan over a wider range of relative humidity (40-90%). Notably, the composite has shown adsorption selectivity toward ethyl mercaptan compared to hydrogen sulfide and other reducing or oxidizing analytes. Moreover, a density functional theory (DFT) study has been performed to understand the adsorption selectivity, charge transfer, and modification in the electronic properties after molecule adsorption on the host surface. Simulations predicted the lowest negative adsorption energy for ethyl mercaptan, implying the chemisorption (-142.029 kJ mol-1) process of adsorption. The device thus-obtained has also shown a stable response even at an extreme relative humidity level of 90%. The obtained results and superior signal-to-noise ratio indicate that a MoSe2/SnO2-based sensor may be a promising candidate for highly selective and sensitive detection of ethyl mercaptan even below 1 ppm.

MoSe2/multiwalled carbon nanotube composite for ammonia sensing in natural humid environment.

Herein, we report ammonia sensing in a natural highly humid environment using MoSe2/multi-walled carbon nanotube (MWCNT) composite as sensing platform. The composite synthesis involved two steps, in the first step, MWCNTs were treated in an acidic medium to obtain -COOH group functionalized MWCNTs. In the second step, functionalized MWCNTs were probe sonicated with MoSe2 to obtain MoSe2/MWCNT composite. Proposed device exhibited superior sensing properties at a temperature down to 16∘ C and relative humidity of 80%. Under these extreme natural environmental conditions, the device exhibited a relative response of 21% for 0.5 ppm of ammonia and superior noise free signal further suggests their use even below this concentration. Composite based device has also displayed better adsorption selectivity towards NH3 as compared with other reducing and oxidizing gas molecules. Density functional theory simulations were further employed to understand the underlying adsorption process and selectivity behavior of the composite. Simulations predicted lowest negative adsorption energy for ammonia, implying physisorption (-0.387 eV) type exothermic adsorption process. Present results indicate that a composite with the rightly engineered MoSe2 and MWCNTs weight ratio may serve as a potential candidate for ammonia sensing in a highly humid environment.

Solvent Effects on the Photophysical Properties of a Donor-acceptor Based Schiff Base.

In this work, a donor-acceptor substituted aromatic system ((E)-N-((E)-3-(4 (dimethylamino)phenyl) allylidene)-4-(trifluoromethyl) benzenamine (DPATB) has been synthesized and its detailed photophysics of intramolecular charge transfer process have been explored on the basis of steady state absorption, fluorescence and time resolved spectroscopy in combination with density functional theory calculations. Large solvent dependency fluorescence spectral shift and the calculated large excited state dipole moment clearly indicate an efficient charge transfer occurring from the donor group to the acceptor moiety in the excited state. Effect on addition of acid and pH on steady state spectral properties further reveals excited state charge transfer character. Quantum chemical calculations were performed in order to study the conformation and polarity of DPATB at their ground as well as excited electronic states. The HOMO and LUMO molecular orbital pictures are obtained at DFT level using B3LYP functional and 6-311 + g(d,p) basis set which clearly support excited state intramolecular charge transfer process. The molecular electrostatic potential maps for the optimized ground state, donor twisted and acceptor twisted geometry shed insight on the electrostatic potential and charge distribution in a system which gives information about the reacting site of the probe and nature of the reaction. In this work, detailed photophysics of excited state intramolecular charge transfer process in donor-acceptor system (DPATB) was evaluated using steady state and time-resolved fluorescence spectroscopy in combination with density functional theory calculations. Large solvent dependency fluorescence spectral shift and the calculated large excited state dipole moment clearly indicate an efficient charge transfer occurring in DPATB. Molecular orbital pictures as obtained from DFT based computational analysis reveals a significant change in the distribution of electron density upon transition from HOMO to LUMO which confirms an ICT process occurring from the donor group to the acceptor moiety in the excited state.

Electronic and transport property of two-dimensional boron phosphide sheet.

Using density functional theory (DFT) approach, we have investigated the effect of strain on the electronic properties of two-dimensional (2D) boron phosphide (BP) sheet. With the increase in uniaxial and biaxial tensile strain band gap increases while band gap decreases and becomes metallic with the increase in uniaxial and biaxial compressive strain. Electrical and thermal transport properties of zigzag and armchair 2D BP sheets have been explored using nonequilibrium Green's function formalism (NEGF) and the changes in the nature of I-V characteristics with the application of strain have been reported. The magnitude of the current decreases with the increase of strain value along transport direction for both zigzag and armchair 2D BP sheets. For unstrained systems, the magnitude of current is nearly same for both zigzag and armchair 2D BP sheets. However, for a particular strain value, magnitude of current is more for zigzag sheet compared to armchair sheet. Though both zigzag and armchair 2D BP sheets have reasonably high ZTe which confirms its potentiality for designing efficient thermoelectric material but zigzag sheet is more preferable for thermoelectric application compared to armchair sheet due to its higher ZTe in comparison to armchair sheet.

Thermoelectric Properties of Pristine Graphyne and the BN-Doped Graphyne Family.

In this paper, we have investigated the thermoelectric properties of BN-doped graphynes and compared them with respect to their pristine counterpart using first-principles calculations. The effect of temperature on the thermoelectric properties has also been explored. Pristine γ-graphyne is an intrinsic band gap semiconductor and the band gap significantly increases due to the incorporation of boron and nitrogen atoms into the system, which simultaneously results in high electrical conductivity, a large Seebeck coefficient, and low thermal conductivity. The Seebeck coefficient for all these systems is significantly higher than that of conventional thermoelectric materials, suggesting their potential in thermoelectric applications. Among all the considered systems, the "graphyne-like BN sheet" has the highest electrical conductance and lowest thermal conductance, ensuring its superiority in thermoelectric properties over the other studied systems. We find that a maximum full ZT of ∼6 at room temperature is accessible in the "graphyne-like BN sheet".

Designing nanoscale capacitors based on twin-graphene.

A 'twin-graphene' bilayer-based nanoscale capacitor and nanoscale dielectric capacitor are designed using a density functional theory approach including van der Waals dispersion correction. A strong effect on electronic properties is observed for different stacking modes. The AB stacking mode is the most stable one among the considered stacking modes with a band gap of 0.553 eV. Our predicted energy and charge-storage capacities are higher than those of other nanoscale capacitors designed using other two-dimensional carbon allotropes. We designed a nanoscale dielectric capacitor by placing a 'twin-graphene like BN sheet' (n = 1-3) sandwiched between 'twin-graphene' layers. The capacitance decreases significantly in the nanoscale dielectric capacitor model compared to the nanoscale capacitor model. However, the measured capacitance is higher than that of the previously studied nanoscale dielectric capacitor models. The significant capacitance of our proposed models ensures their promising applications for designing next-generation nanoscale capacitors.

Reactivity Dynamics.

The chemical reactivity of a molecule as a whole or of an atom in a molecule varies during a chemical reaction. A variation of global and local reactivity descriptors in the course of a physicochemical process was studied within a quantum fluid density functional theory framework. Effects of a physical confinement and the electronic excitation therein were studied. In this Perspective, we also highlight the direction of a spontaneous chemical reaction in the light of the dynamical variants of the conceptual density functional theory-based electronic structure principles. An exhaustive state-of-the-art dynamical study is warranted in order to understand a chemical reaction from a reactivity perspective augmenting the associated molecular reaction dynamics analysis.

Confinement Effects of a Noble Gas Dimer Inside a Fullerene Cage: Can It Be Used as an Acceptor in a DSSC?

A detailed density functional theory investigation of He2-encapsulated fullerene C36 and C40 has been presented here. When confinement takes place, He-He bond length shortens and a non-covalent type of interaction exists between two He atoms. Energy decomposition analysis shows that though an attractive interaction exists in free He2, when it is confined inside the fullerenes, repulsive interaction is observed due to the presence of dominant repulsive energy term. Fullerene C40, with greater size, makes the incorporation of He2 much easier than C36 as confirmed from the study of boundary crossing barrier. In addition, we have studied the possibility of using He2-incorporated fullerene as acceptor material in dye-sensitized solar cell (DSSC). Based on the highest energy gap, He2@C40 and bare C40 fullerenes are chosen for this purpose. Dye constructed with He2@C40 as an acceptor has the highest light-harvesting efficiency and correspondingly will possess the maximum short circuit current as compared to pure C40 acceptor.

Theoretical study of electronic transport through P-porphyrin and S-porphyrin nanoribbons.

Electronic transport through P-porphyrin and S-porphyrin nanoribbons have been studied by using nonequilibrium Green's function formalism (NEGF) combined with density functional theory (DFT) method. Band structure of both nanoribbons shows metallic behavior and bands near the Fermi level contain π character contributed by py orbital. Both nanoribbons exhibit metal-like conduction at extreme low bias. A remarkable negative differential resistance (NDR) effect is observed for both nanoribbons which is further explained with the evolution of transmission peak within energy bias window (EBW), and overlap of energy states of left and right electrodes. The low bias NDR phenomena of our proposed devices could be used in designing NDR devices including frequency multipliers, memory, and fast switches.

Density Functional Theory Investigation of Nonlinear Optical Properties of T-Graphene Quantum Dots.

Using density functional theory calculations, we have analyzed nonlinear optical properties of a series of T-graphene quantum dots differing in their shape and size. Electronic polarizability and first-order and second-order hyperpolarizability of these systems are investigated and shed light on their stability and electronic properties. Negative cohesive energy shows that they are energetically stable. The effect of size and incident frequency on their nonlinear responses are comprehensively discussed. Most of the systems exhibit a strong NLO response, and it is enhanced in the presence of an external field. All these systems show absorption maximum ranging from UV to visible window. Overall, this theoretical framework highlighted the nonlinear optical properties of T-graphene quantum dots that may provide valuable information in designing potential NLO materials.

Non-covalent interactions between epinephrine and nitroaromatic compounds: A DFT study.

Here, we present a density functional theory (DFT) study of hydrogen bonding and π-π stacking interactions between epinephrine and different aromatic nitro-compounds in gas phase as well as in methanol solvent. Detail investigations of hydrogen bonding and π-π interactions are performed and confirmed on the basis of theoretical IR spectra, natural bond orbital (NBO) analysis, non-covalent interaction (NCI), chemical reactivity descriptors and electronic spectra. Among different functionals used for the calculation, the results obtained from ωB97XD functional are found to be more suitable to describe the hydrogen bonding and π-π stacking phenomenon for our considered systems. Weakening of hydrogen bonding and π-π stacking interaction on solvent incorporation is observed. Electronic transition between different orbitals and transition probabilities of epinephrine and nitro-aromatic complexes are described using time dependent density functional theory (TD-DFT) method.

The spin filtering effect and negative differential behavior of the graphene-pentalene-graphene molecular junction: a theoretical analysis.

Density functional theory (DFT) combined with nonequilibrium Green's function (NEGF) formalism are used to investigate the effects of substitutional doping by nitrogen and sulfur on transport properties of AGNR-pentalene-AGNR nanojunction. A considerable spin filtering capability in a wide bias range is observed for all systems, which may have potential application in spintronics devices. Moreover, all model devices exhibit a negative differential effect with considerable peak-to-valley ratio. Thus, our findings provide a way to produce multifunctional spintronic devices based on nitrogen and sulfur doped pentalene-AGNR nanojunctions. The underlying mechanism for this interesting behavior was exposed by analyzing the transmission spectrum as well as the electrostatic potential distribution. In addition, a system doped with an odd number of dopant shows a rectifying efficiency comparable to other systems. The above findings strongly imply that such a multifunctional molecular device would be a useful candidate for molecular electronics. Graphical abstract The graphene-pentalene-graphene molecular junction.

Characterizing the sensitivity of bonds to the curvature of carbon nanotubes.

The way the bonding and reactivity of armchair carbon nanotubes depends on the curvature of the nanotube has been investigated using density functional theory. To understand the nature of the interaction between atoms in the nanotube, the Wiberg bond index, natural bond order analysis, and topological electron density analysis have been performed. All these tools confirm that the bonds in the hydrogen-capped carbon nanotubes considered here are primarily covalent. As the diameter of the nanotube decreases and its curvature increases, the covalency (bond order) decreases, a conclusion that is supported by the increase of the bond lengths and also the decrease of the electron density and the energy density along the bond paths as the curvature increases. To shed light on the orbital contribution in bond formation and the most effective interaction between donor bonding orbital and acceptor antibonding orbital, analysis of natural bond orbitals is carried out. We have observed that the higher the nanotube diameter is, the higher the energy gap.

Electronic and optical properties of C24, C12X6Y6, and X12Y12 (X = B, Al and Y = N, P).

Utilizing first-principles calculations, we studied the electronic and optical properties of C24, C12X6Y6, and X12Y12 fullerenes (X = B, Al; Y = N, P). These fullerenes are energetically stable, as demonstrated by their negative cohesive energies. The energy gap of C24 may be tuned by doping, and the B12N12 fullerene was found to have the largest energy gap. All of the fullerenes had finite optical gaps, suggesting that they are optical semiconductors, and they strongly absorb UV radiation, so they could be used in UV light protection devices. They could also be used in solar cells and LEDs due to their low reflectivities. Graphical abstract Possible applications of doped C24 fullerene.

Structure, vibrational, and optical properties of platinum cluster: a density functional theory approach.

Using density functional theory, stability, chemical, and optical properties of small platinum clusters, Ptn (n = 2 to 10) have been investigated. An attempt has been made to establish a correlation between stability and chemical reactivity parameters. The calculated geometries are in agreement with the available experimental and theoretical results. The atom addition energy change (ΔE1) and stability function (ΔE2) reveal that Pt7 is more stable than its neighboring clusters. Very good agreement of the calculated electron affinity with the available experimental results has been observed. The polarizability of the Ptn clusters depends almost linearly on the number of atoms. A correlation between the static polarizability and ionization potential is found, paving a way to calculate polarizabilty of larger clusters from their ionization potential. The calculated vibrational frequencies are compared with available experimental and theoretical results and good agreement between them has been established. In general, the prominent peak of molar absorption coefficient is shifting toward the lower energy side when cluster size grows. Our DOS calculation suggests that d orbital is primarily responsible for HOMO position and s orbital is responsible for LUMO position.