Search

Effects of Mo-vacancy concentration on the structural, electronic and optical properties of monolayer MoS 2 have been investigated using the first-principles calculations. Results show that Mo-vacancy is prone to form in monolayer MoS 2 under S-rich condition. S atoms around Mo-vacancy exhibit an outward relaxation, whereas Mo atoms around Mo-vacancy show an inward relaxation. At low Mo-vacancy concentration, some localized impurity states are induced in the band gap of monolayer MoS 2 , coupled with a band gap increment. As the Mo-vacancy concentration increases, the impurity states become delocalized and mix with the upper valence bands, resulting in the band gap decrease. The covalent character of Mo-S bonding is enhanced upon the introduction of Mo-vacancy, and the enhancement is weakened as the Mo-vacancy concentration increases. Optical properties calculations show that the static dielectric constant increases with the increasing Mo-vacancy concentration. The imaginary part of complex dielectric function exhibits a little blue shift for monolayer MoS 2 with low Mo-vacancy concentration, whereas the imaginary part of complex dielectric function shows distinct red shift for monolayer MoS 2 with high Mo-vacancy concentration. [ABSTRACT FROM AUTHOR]

The formation energies of intrinsic vacancies in monolayer MoS 2 as well as effect of the vacancies on electronic structures of monolayer MoS 2 were investigated using the first-principles density functional theory. Results show that both Mo and S vacancies depend greatly on the Fermi level. With the increasing Fermi level, the formation energies of S vacancies increase whereas the formation energies of Mo vacancies decrease. Under reducing conditions, S vacancies are more likely to form and V S 2 + is the dominant defect. In contrast, under oxidizing conditions, Mo vacancies are easier to form and V Mo 4 − is the main source of defect. After introducing the intrinsic vacancies, the valence and conduction bands of monolayer MoS 2 were expanded toward lower energy and the band gaps of monolayer MoS 2 were decreased. Moreover, V Mo 4 − brings about deep acceptor-like levels and p-type conductivities, whereas V S 2 + induces deep donor-like levels and n-type conductivities. [ABSTRACT FROM AUTHOR]

Highlights: [•] B, E and v increase as pressure increases, except for a sudden decrease at 40GPa. [•] WSe2 under pressure has larger shear modulus and higher hardness than WSe2 at 0GPa. [•] WSe2 has an isostructural semiconductor-semimetal phase transition at 40GPa. [•] The covalent bonding between Se and W atoms in the slabs is enhanced under pressure. [•] The distance of the stacked Se–W–Se slabs is decreased with the increasing pressure. [Copyright &y& Elsevier]

We have systematically studied the adsorption of thiocyanate (SCN−) on gold-core palladium-shell nanoparticles (Au@Pd NPs) with different Pd shell thicknesses by surface-enhanced Raman scattering (SERS). When the Pd shell thickness is increased from one to ten atomic layers, the νC—N stretching frequency increases 6 cm−1 for S-bound SCN− and 10 cm−1 for N-bound SCN−. It infers that the C—N stretching frequency is quite sensitive to electronic properties of the NP surface, but even more so when bonding to Pd occurs through the N atom (at negative potentials) than when it occurs through the S atom (at positive potentials). Data for a second probe, p-aminothiophenol (PATP), was compared to that of SCN−; however, PATP was found to be less sensitive than SCN− to the surface electronic properties of Au@Pd NPs. [ABSTRACT FROM AUTHOR]

Abstract: The first-principles calculations were carried out to investigate the electronic and optical properties of Pbnm orthorhombic SrHfO3. The equilibrium lattice constants of Pbnm orthorhombic SrHfO3 optimized by the localized density approximation (LDA) are in good agreement with experimental values. Electronic structures of Pbnm orthorhombic SrHfO3 have been studied throughout the calculations of band structure, densities of states (DOS) and charge densities. The band structure shows that Pbnm orthorhombic SrHfO3 has direct band gap. The DOS and charge densities of Pbnm orthorhombic SrHfO3 indicate that bonding between Hf and O is mainly covalent whereas bonding between Sr and O is mainly ionic. The complex dielectric function, refractive index, absorption coefficient, energy-loss spectrum, complex conductivity function and reflectivity of Pbnm orthorhombic SrHfO3 have been predicted. The imaginary and real parts of the calculated complex dielectric function are consistent with the experimental measurements for the amorphous SrHfO3. [ABSTRACT FROM AUTHOR]

Abstract: Ab initio calculations are used to investigate the electronic structure and optical properties of crystalline monoclinic hafnium silicates (Hf1− x Si x O2) as a function of silicon content x (x =0, 0.25, 0.50, and 0.75). Densities of states (DOS), electronic band gaps, refractive indices and extinction coefficients of Hf1− x Si x O2 are calculated through a screened exchange (sX) method within the local density approximation (LDA). Calculational results of the DOS of Hf1− x Si x O2 indicate that these oxides are insulators. Electronic band gaps of Hf1− x Si x O2 are found to increase with increasing the silicon content. The results of optical constants of Hf1− x Si x O2 show that increasing silicon content produces a lower refractive index and a smaller extinction coefficient. The present predicted results exhibited a good agreement with the recently reported experimental observations. [Copyright &y& Elsevier]

Abstract: The plane-wave ultrasoft pseudopotential technique based on the first-principles density-functional theory (DFT) is used to investigate the doping effect of N substituting for O in cubic SrHfO3. The calculated results show that the reaction from pure elements to final compounds is favorable and the final compounds are energetically stable. Electronic structure analysis shows the band gaps narrowing with the increase of N concentration due to the presence of the impurity state of N 2p on the top of the valence band and the acceptor energy levels above the Fermi energy, which may be responsible for the red-shift. Besides, the optical absorption edge has been gradually red shifted with increasing N concentration. [Copyright &y& Elsevier]

Abstract: We have performed the ab initio total energy calculations using the plane-wave ultrasoft pseudopotential technique based on the first-principles density-functional theory (DFT) to study the structural parameters, elastic, electronic, chemical bonding and optical properties of orthorhombic NaAlF4. The calculated lattice parameters are in good agreement with experimental work. The bulk, shear and Young’s modulus, Poisson’s coefficient, compressibility and Lamé’s constants are firstly obtained using Voigt–Reuss–Hill method and the Debye temperature is estimated using Debye-Grüneisen model. Band structure shows a direct band gap at Γ point. Density of states and charge density have been studied, which show the bonding between Na and F is mainly ionic as well as that between Al and F. In order to clarify the mechanism of optical transitions of orthorhombic NaAlF4, the complex dielectric function, refractive index, extinction coefficient, reflectivity, absorption efficient, loss function and complex conductivity function are calculated. The optical properties and origins of the structure have been analysed. [Copyright &y& Elsevier]

Abstract: We have performed ab-initio total energy calculations using the plane-wave ultrasoft pseudopotential technique based on the first-principles density-functional theory (DFT) to study structural parameters, mechanical, electronic structure, chemical bonding and optical properties of orthorhombic GaPO4. The calculated lattice parameters are in agreement with previous experimental work. The independent elastic constants, bulk, shear and Young’s modulus, Poisson coefficient, compressibility and Lamé constants are obtained using Voigt–Reuss–Hill method. Electronic and chemical bonding properties have been studied from the calculations of band structure, density of states and charge densities. Furthermore, in order to clarify the mechanism of optical transitions of orthorhombic GaPO4, the complex dielectric function, refractive index, extinction coefficient, reflectivity, absorption efficient, loss function and complex conductivity function are calculated. [Copyright &y& Elsevier]

Abstract: Structural parameters as well as elastic, electronic, bonding and optical properties of monoclinic ZrO2 were investigated using the plane-wave ultrasoft pseudopotential technique based on the first-principles density-functional theory (DFT). The calculated structural properties and independent elastic constants of monoclinic ZrO2 are in favorable agreement with previous work. We have derived the bulk and shear moduli, Young’s modulus and Poisson coefficients for monoclinic ZrO2 and estimated the Debye temperature of monoclinic ZrO2 from acoustic velocity. Electronic and bonding properties are studied from the calculation of band structure, densities of states and charge densities. Furthermore, in order to clarify the mechanism of optical transitions in monoclinic ZrO2, the dielectric functions are calculated and analyzed by means of the electronic structure, which shows significant optical anisotropy in the components of polarization directions (100), (010) and (001). [ABSTRACT FROM AUTHOR]

Abstract: HfTaO3N is an important material in the future industrial applications. However, there are no data in the literature about these analysis. In this paper, structural parameters, elastic, electronic and bonding properties of HfTaO3N have been investigated using the plane-wave ultrasoft pseudopotential technique based on the first-principles density-functional theory (DFT). These properties of HfTaO3N have been firstly theoretically predicted, which await experimental confirmation. [ABSTRACT FROM AUTHOR]

Abstract: Structural parameters, elastic, electronic, bonding and optical properties of rutile GeO2 and α-quartz GeO2 have been investigated using the plane-wave ultrasoft pseudopotential technique based on the first-principles density functional theory (DFT). The ground-state properties obtained by minimizing the total energy are in favorable agreement with the previous work. Two phases of GeO2 are found to be elastically stable and we have derived the bulk, shear and Young’s modulus, Poisson coefficient for rutile GeO2 and α-quartz GeO2. We estimated the Debye temperature of rutile GeO2 and α-quartz GeO2 from the acoustic velocity. Electronic and chemical bonding properties have been studied from the calculation of band structure, density of states and charge densities. Furthermore, in order to clarify the mechanism of optical transitions for rutile GeO2 and α-quartz GeO2, the complex dielectric function, refractive index, extinction coefficient, optical reflectivity, absorption coefficient, energy-loss spectrum and the complex conductivity function are calculated, which show the significant optical anisotropy in the components of polarization directions (100) and (001) for rutile GeO2 and α-quartz GeO2. [ABSTRACT FROM AUTHOR]

Abstract: We have performed ab-initio total energy calculations using the plane-wave ultrasoft pseudopotential technique based on the first-principles density-functional theory (DFT) to study structural parameters, mechanical, electronic, chemical bonding and optical properties of cubic BaHfO3. The calculated lattice parameter and independent elastic constants are in good agreement with previous theoretical and experimental work. The bulk, shear and Young’s modulus, Poisson coefficient, compressibility and Lamé constants are obtained using Voigt–Reuss–Hill method and the Debye temperature is estimated using Debye–Grüneisen model, which are consistent with previous results. Electronic and chemical bonding properties have been studied from the calculations of band structure, density of states and charge densities. Furthermore, in order to clarify the mechanism of optical transitions of cubic BaHfO3, the complex dielectric function, refractive index, extinction coefficient, reflectivity, absorption efficient, loss function and complex conductivity function are calculated. Then, we have explained the origins of spectral peaks on the basis of the theory of crystal-field and molecular-orbital bonding. [ABSTRACT FROM AUTHOR]

Abstract: Structural parameters, elastic, electronic, chemical bonding and optical properties of γ-TeO2 are investigated using the plane-wave ultrasoft pseudopotential technique based on the first-principles density-functional theory (DFT). The calculated equilibrium lattices are in reasonable agreement with the experimental results. We have obtained the bulk, shear and Young’s modulus, Poisson coefficient for γ-TeO2. Electronic and chemical bonding properties have been studied throughout the calculation of band structure, density of states and charge densities. Moreover the complex dielectric function, refractive index, extinction coefficient, absorption efficient, reflectivity, loss function and complex conductivity function are calculated, which show a significant optical anisotropy in the components of polarization directions (100), (010) and (001). [Copyright &y& Elsevier]

Abstract: Structural parameters, elastic, electronic, bonding and optical properties of delafossite CuAlO2 have been investigated using the plane-wave ultrasoft pseudopotential technique based on the first-principles density-functional theory (DFT). The ground-state properties obtained by minimizing the total energy are in favorable agreement with the previous work. We have derived the bulk, shear and Young''s modulus, Poisson coefficient for delafossite CuAlO2. We estimated the Debye temperature of CuAlO2 from the acoustic velocity. Electronic and chemical bonding properties have been studied throughout the calculation of band structure, density of states and charge densities. Furthermore, in order to clarify the mechanism of optical transitions for delafossite CuAlO2, the dielectric function is calculated, which shows a significant optical anisotropy in the components of polarization directions (100) and (001). [Copyright &y& Elsevier]

Abstract: The structural, electronic and optical properties of tetragonal SnO2 and SnO were investigated by the plane-wave ultrasoft pseudopotential technique based on the first-principles density-functional theory (DFT). The calculated structural parameters are in good agreement with previous calculation and experimental data. The energy band structures, density of states and charge densities are calculated and analyzed. The calculated carrier effective masses are shown to be anisotropic. Furthermore, in order to understand the optical properties of tetragonal SnO2 and SnO, the complex dielectric function, refractive index, extinction coefficient, reflectivity, absorption efficient, loss function and complex conductivity function are calculated for radiation up to 40eV. We have explained the origin of the spectral peaks on the basis of the theoretics about crystal-field and molecular-orbital bonding. [Copyright &y& Elsevier]

Abstract: Structural, electronic and chemical bonding properties of the (001) surface of cubic SrHfO3 have been investigated with both SrO and HfO2 termination using the plane-wave ultrasoft pseudopotential technique based on the first-principles density-functional theory. The relaxed structures of two slabs have been analyzed, which shows the interplanar distance of two slabs has the same changed trend. The electronic band structures and density of states of two slabs have been discussed, showing the reduced band gaps by comparison with those of bulk system. The chemical bonding between Sr and O between the surface layer and subsurface layer as well as Hf and O has been increased. The surface energy, work function and stability have been calculated, which indicates SrO-terminated slab is more stable. [Copyright &y& Elsevier]

Abstract: Structural parameters, elastic, electronic, bonding and optical properties of zinc-blende and rocksalt GeC have been investigated using the plane-wave ultrasoft pseudopotential technique based on the first-principles density-functional theory (DFT). The ground-state properties obtained by minimizing the total energy are in favorable agreement with the previous work. Two phases of GeC are found to be elastically stable and we have obtained the bulk, shear and Young’s modulus, Poisson’s coefficient and Lamé’s constants for zinc-blende and rocksalt GeC. We estimated the Debye temperature of zinc-blende and rocksalt GeC from the acoustic velocity. Electronic and chemical bonding properties have been studied. Moreover, the complex dielectric function, refractive index, extinction coefficient, optical reflectivity, absorption coefficient, energy-loss spectrum and the complex conductivity function are calculated. [Copyright &y& Elsevier]

Abstract: We calculated the structural parameters, elastic, mechanical, electronic and optical properties of 3R- and 2H-CuGaO2 using the first-principles density-functional theory. The results show that the structural parameters of two phases are in good agreement with previous theoretical and experimental data. Two phases are mechanically stable, behave in ductile manner and have indirect band gap. The analyses of electronic structures and charge densities of two phases show mainly covalent nature in Cu–O bonds and coexistence of both ionic and covalent nature in Ga–O bonds. The optical properties are obtained and discussed, including the complex dielectric function, refractive index, extinction coefficient, optical reflectivity, absorption coefficient, energy-loss spectrum and complex conductivity function, which provide useful information for the future applications of CuGaO2. [Copyright &y& Elsevier]

Abstract: We have investigated the structural parameters, electronic structure and optical properties of orthorhombic SrZrO3 using the plane-wave ultrasoft pseudopotential technique based on the first-principles density-functional theory (DFT). Our calculated structural parameters are in good agreement with the previous theoretical and experimental data. Band structure, density of states and chemical bonding have been systematically studied. Furthermore, the complex dielectric function, refractive index, extinction coefficient, optical reflectivity, absorption coefficient, loss function and optical conductivity are calculated, which show an optical anisotropy in the components of polarization directions (100), (010) and (001). [ABSTRACT FROM AUTHOR]