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Effects of spin-orbit coupling on the optical response of a material
摘要： We investigate the effects of spin-orbit coupling on the optical response of materials. In particular, we study the effects of the commutator between the spin-orbit coupling part of the potential and the position operator on the optical matrix elements using density functional theory calculations within the generalized gradient approximation. By means of a formalism that separates a fully relativistic Kleinman-Bylander pseudopotential into the scalar-relativistic and spin-orbit-coupling parts, we calculate the contribution of the commutator arising from spin-orbit coupling to the squared optical matrix elements of isolated atoms, monolayer transition-metal dichalcogenides, and topological insulators. In the case of isolated atoms from H (Z = 1) to Bi (Z = 83), the contribution of spin-orbit coupling to the squared matrix elements can be as large as 14%. On the other hand, in the cases of monolayer transition-metal dichalcogenides and topological insulators, we find that this contribution is less than 1% and that it is sufficient to calculate the optical matrix elements and subsequent physical quantities without considering the commutator arising from spin-orbit coupling.
关键词： optical response,spin-orbit coupling,transition-metal dichalcogenides,topological insulators,density functional theory
更新于2025-09-04 15:30:14
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Hyperelastic material modeling of graphene based on density functional calculations
摘要： A new parameter set for the graphene material model of [1] is obtained. The material model is anisotropic hyperelastic and calibrated by a trial dataset generated by density functional theory (DFT). The DFT experiments are one pure dilatation test and two uniaxial stretch tests along the armchair and zigzag directions. The strain energy is computed from ab-initio simulations and used to calibrate the parameters of the hyperelastic model. The strain energy and stresses from the new parameter set are calculated and verified with the results of [1].
关键词： density functional theory,hyperelastic material model,DFT,anisotropic,strain energy,graphene
更新于2025-09-04 15:30:14
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Electron/Energy Transfer Studies on Hybrid Materials Based on Dinuclear Coordination Compounds of Twisted Perylene Diimide
摘要： To understand the influence of transition metal ion coordination on the properties and performance of the triads, the symmetric bridging ligand, 1,10-phenanthroline-perylene diimide-1,10-phenanthroline, 1,10-Phen-PDI-1,10-Phen (1) comprising four electron-donating 4-methoxyphenoxy bulky groups at bay-positions and its corresponding square-planar coordination compounds with dichloroplatinum(II), [{PtCl2}2-1] (2) and palladium(II) [{PdCl2}2-1] (3) were prepared in order to tune the photochemical and optical properties of these hybrid materials. These triads show strong electronic absorption bands attributed to the PDI and M(II)(1,10-Phen)Cl2 moieties in DMSO. UV-Vis absorption spectra of compounds were calculated using Time-Dependent Density Functional Theory (TDDFT) for the ground state optimized structures in DCM. Current results indicate that 2 has the lowest HOMO-LUMO gap (2.29 eV in DCM) among the investigated molecules. The energy and charge transfer processes with tailoring molecular structures are one of the important strategies for the design of future functional triads based on donor and acceptor moieties for hybrids optoelectronic devices. Thus, we studied linear absorption, fluorescence, and ultrafast transient absorption spectra measurements for the triads in dichloromethane to investigate the impact of different functionalization strategies on the optical characteristics, photo-stability, and photo-induced charge-transfer (CT) processes. The observed ultrafast intramolecular charge transfer from donor units to acceptor part of 1, 2 and 3 is related to fluorescence quenching and faster singlet state decay on transient absorption measurements. The intramolecular charge transfer mechanism was also compared with the unsymmetrical counterparts that were investigated previously. Symmetrical compounds exhibit faster charge transfer in comparison with the unsymmetrical compounds.
关键词： density functional theory,coordination compounds,ultrafast pump-probe,Perylene diimide,hybrid materials
更新于2025-09-04 15:30:14
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Energy Band Gap Modulation in Nd-doped BiFeO <sub/>3</sub> /SrRuO <sub/>3</sub> Heteroepitaxial for Visible Light Photoelectrochemical Activity
摘要： The ability of band offsets at multiferroic/metal and multiferroic/electrolyte interfaces in controlling charge transfer, and thus alters the photoactivity performance has sparked significant attention in solar energy conversion applications. Here, we demonstrate that the band offsets of the two interfaces play the key role in determining charge transport direction in a downward self-polarized BFO film. Electrons tend to move to BFO/electrolyte interface for water reduction. Our experimental and first-principles calculations reveal that the presence of neodymium (Nd) dopants in BFO enhances the photoelectrochemical performance by reduction of the local electron-hole pair recombination sites and modulation of the band gap to improve the visible light absorption. This opens a promising route to the heterostructure design by modulating the band gap to promote efficient charge transfer.
关键词： density functional theory (DFT),heterojunction band offsets,charge transfer,Nd-doped BiFeO3,photoelectrochemical (PEC)
更新于2025-09-04 15:30:14
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Prediction of Adsorption Probability of Oxidizing and Reducing Species on 2D Hybrid Junction of rGO-ZnO from First Principle Analysis
摘要： The target of this paper is to theoretically investigate the probability of gas (both oxidizing and reducing) adsorption on the van der Waals (vdW) heterojunction formed between p-type rGO and n-type 2D-ZnO, using density functional theory (DFT) based first principle calculation employing Virtual Nanolab (VNL) Atomistix Toolkit (ATK) (v2016.4). Two types of heterostructures are considered viz. heterostructure type-1 where hydroxyl group (sp2) is at the edge of the reduced graphene oxide (rGO) and heterostructure type-2 where hydroxyl group (sp3) is perpendicular to the plane of rGO. Adsorption energy, charge transfer and the distance of the nearest atom from the adsorbent are calculated for oxidizing (NO2 as the test case) and reducing (NH3 as the test case) species and compared with that of Oxygen on rGO/2D-ZnO heterostructures as well as on its individual constituent (rGO nanoflakes and 2D-ZnO, separately). Like 2D-ZnO, heterostructure type-1 was also found to be selective towards NO2 with almost three times and five times higher adsorption energy than that of 2D-ZnO and rGO, respectively. On the other hand, it was found that charge distribution in the underlying 2D-ZnO of heterostructure type-2 remained almost unaltered even after gas adsorption and therefore lead to insignificant improvement compared to its 2D-ZnO counterpart.
关键词： gas adsorption probability,charge transfer,van der Waals heterostructure,Density functional theory,rGO-ZnO hybrid system
更新于2025-09-04 15:30:14
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monolayers on the hBN-layer thickness
摘要： The optical properties of two-dimensional transition-metal dichalcogenide monolayers, such as MoS2 or WSe2 are dominated by excitons, Coulomb bound electron-hole pairs. Screening effects due to the presence of hexagonal-boron nitride (hBN) surrounding layers have been investigated by solving the Bethe-Salpeter equation on top of GW wave functions in density functional theory calculations. We have calculated the dependence of both the quasiparticle gap and the binding energy of the neutral exciton ground-state Eb as a function of the hBN-layer thickness. This paper demonstrates that the effects of screening at this level of theory are more short ranged than is widely believed. The encapsulation of a WSe2 monolayer by three sheets of hBN (～1 nm) already yields a 20% decrease in Eb, whereas the maximal reduction is 27% for thick hBN. We have performed similar calculations in the case of a WSe2 monolayer deposited on stacked hBN layers. These results are compared to the recently proposed quantum electrostatic heterostructure approach.
关键词： GW wave functions,density functional theory,hexagonal-boron nitride,two-dimensional transition-metal dichalcogenide,Bethe-Salpeter equation,exciton
更新于2025-09-04 15:30:14
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Effect of excess electron on structure, bonding, and spectral properties of sulfur/selenium based dichalcogen systems
摘要： First principle based quantum chemical methods are employed to characterize structure, bonding, and spectral properties of sulfur and selenium based dichalcogen systems in presence of an excess electron. Inter molecular two-center three-electron (2c-3e) bonding between two chalcogen (X) atoms is described in the systems of the type (R-X)2?- (R = Ph, PhCH2 X = S, Se). In addition, effect of electron withdrawing (-NO2) and electron donating (-CH3) groups in phenyl ring on the stability of these 2c-3e bonded systems is also studied in water medium applying a macroscopic hydration model. Molecular parameters and binding energy of the neutral, (R-X)2 and reduced, (R-X)2?- dichalcogen systems are compared. Search for minimum energy structures of these open shell doublet systems are carried out applying various density functionals with dispersion corrections and MP2 method considering 6-311++G (d,p) set of basis functions for all atoms. Effect of water medium is introduced through a macroscopic solvation model based on density (SMD). Frontier molecular orbitals based analysis is carried out for showing the definite presence of 2c-3e bond between two chalcogen atoms in these radical anions of sulfur and selenium based aromatic dichalcogen systems. Excited state calculations are performed on all these systems using Time Dependent Density Functional Theory (TDDFT). UV-Vis spectra are simulated and effect of solvent water on the absorption maximum of these radical anions is discussed. This study illustrates that the combination of electronic effect and geometrical flexibility decides the strength of two-center three-electron bond in these systems.
关键词： sulfur,hemi bond,radical anion,density functional theory,chalcogen,excess electron,2c-3e bond,antioxidant,selenium
更新于2025-09-04 15:30:14
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Formation mechanism of twin domain boundary in 2D materials: The case for WTe2
摘要： Our scanning tunneling microscopy (STM) study observes, for the first time, twin domain boundary (TDB) formations on the surface of WTe2 single crystal, which is glued by solidifying indium to Si substrate. In these TDB regions, a large inhomogeneous strain field, especially a critical shear strain of about 7%, is observed by geometric phase analysis. This observation does not obey the old believe that a small mechanical stress is sufficient to drive thermally-induced TDB formations in two-dimensional materials. To resolve the contradiction, we perform density functional theory calculations combined with elasticity theory analysis, which show that TDBs on WTe2 are entirely displacement-induced, for which a critical strain is necessary to overcome the onset barrier.
关键词： WTe2,twin domain boundary,density functional theory,strain,scanning tunneling microscopy (STM)
更新于2025-09-04 15:30:14
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Adsorption properties of O2 on the unequal amounts of binary co-doped graphene by B/N and P/N: A density functional theory study
摘要： Graphene acts as an advanced substrate material, and it has been used as an electrode in fuel cells because it can efficiently adsorb oxygen molecules. In this study, density functional theory (DFT) calculation has been performed to exactly simulate the adsorption and dissociation of oxygen molecules on the XY3-co-doped graphene. The results show that the positively charged P and B atoms act as active sites for oxygen adsorption on the surface of graphene. In addition, PN3-G and NP3-G exhibit higher catalytic activity than the other samples because of the facile transfer of electrons from the highest occupied molecular orbital (HOMO) of O2 to the orbital above the Fermi level in the samples. More interestingly, excessive adsorption leads to the direct dissociation of oxygen molecules and making further dissociation difficult. In conclusion, the adsorption of oxygen molecules at the hollow sites on the PN3-G and NP3-G occurs via the formation of a triangular ring or trans-formation into O2? is proposed as the optimal strategy because these routes are thermodynamically favorable and the associated energy barrier is low. Furthermore, after dissociation, it was found that the oxygen atoms preferably approach the P atom. This work may be useful as a reference for future experimental studies to develop effective metal-free catalysts for fuel-cell cathodes.
关键词： Density functional theory (DFT),XY3 co-doping,Graphene,Electron transfer,Adsorption
更新于2025-09-04 15:30:14
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Tuning the Electronic Structure of Hydrogen-Decorated Silicene
摘要： The effects of strain, charge doping, and external electric field on the electronic structure of a free-standing silicene layer decorated by hydrogen atoms are studied by first-principles density functional theory. Various phases, including insulating, metallic, spin-polarized, and half-metallic have been found, depending on these external factors. The most efficient way of switching the system between these phases is charge doping. The character of the energy gap of the H/silicene system can also be modified, and for charged or for strained systems, the originally indirect gap can be tuned to become direct. The obtained results are very promising in view of the silicene functionalization and potential applications of silicene in the fields of spintronics and optoelectronics.
关键词： density functional theory (DFT),silicene,functionalization
更新于2025-09-04 15:30:14