The electronic and optical properties of TiS2 are studied of density functional theory. A linearized and augmented by using an ab-initio calculation within the frame plane wave basis set with the generalized gradient ...The electronic and optical properties of TiS2 are studied of density functional theory. A linearized and augmented by using an ab-initio calculation within the frame plane wave basis set with the generalized gradient approximation as proposed by Perdew et al. is used for the energy exchange-correlation determination. The results show a metallic character of TiS2, and the plots of total and partial densities of states of TiS2 show the metallic character of the bonds and a strong hybridization between the states d of Ti and p of S below the Fermi energy. The optical properties of the material such as real and imaginary parts of dielectric constant （ε（w） = ε1（w） ＋ iε2（w））, refractive index n（w）, optical reflectivity R（w）, for E / /x and E / /z are performed for the energy range of 0-.14 eV.展开更多
The electronic band structures of wurtzite GaN with Ga and N vacancy defects are investigated by means of the first-principles total energy calculations in the neutral charge state. Our results show that the band stru...The electronic band structures of wurtzite GaN with Ga and N vacancy defects are investigated by means of the first-principles total energy calculations in the neutral charge state. Our results show that the band structures can be significantly modified by the Ga and N vacancies in the GaN samples. Generally, the width of the valence band is reduced and the band gap is enlarged. The defect-induced bands can be introduced in the band gap of GMV due to the Ga and N vacancies. Moreover, the GaN with high density of N vacancies becomes an indirect gap semiconductor. Three defect bands due to Ga vacancy defects are created within the band gap and near the top of the valence band. In contrast, the N vacancies introduce four defect bands within the band gap. One is in the vicinity of the top of the valence band, and the others are near the bottom of the conduction band. The physical origin of the defect bands and modification of the band structures due to the Ga and N vacancies are analysed in depth.展开更多
The structural and electronic properties of sodium bromide （NaBr） are investigated by the density functional theory （DFT） within the generalized gradient approximation （GGA） for the exchange and correlation ener...The structural and electronic properties of sodium bromide （NaBr） are investigated by the density functional theory （DFT） within the generalized gradient approximation （GGA） for the exchange and correlation energy. The equilibrium lattice constant, bulk modulus and its pressure derivative are obtained by fitting the calculated total energy to the third-order Birch-Murnaghan equation of state. The band structure along the higher symmetry axes in the Brillouin zone, the density of states （DOS） and the partial density of states （PDOS） are presented. The results have been discussed and compared with the available experimental and theoretical data.展开更多
Hybrid density functional theory （DFT） calculations are performed to study MC2 （M= V, Cr, Fe and Co） clusters in the neutral and anionic charge states. We find that the equilibrium geometries of MC2 and their anio...Hybrid density functional theory （DFT） calculations are performed to study MC2 （M= V, Cr, Fe and Co） clusters in the neutral and anionic charge states. We find that the equilibrium geometries of MC2 and their anions are all cyclic structures with C2v symmetry, which agrees well with the previous theoretical studies. The Mulliken charge and spin populations of MC2 clusters and their anions are also calculated, and it is found that the electron charge transformations from anions to neutral molecules mainly take place on the M atoms. Time-dependent DFT is used to calculate the excited states, and a theoretical assignment for the features in the experimental photoelectron spectrum is given, which are in good agreement with the available experimental data.展开更多
The lattice parameter, bulk modulus and its pressure derivative of the wurtzite-type aluminium nitride （w-AlN） are investigated by using the Cambridge Serial Total Energy Package （CASTEP） program in the framework ...The lattice parameter, bulk modulus and its pressure derivative of the wurtzite-type aluminium nitride （w-AlN） are investigated by using the Cambridge Serial Total Energy Package （CASTEP） program in the framework of Density Functional Theory （DFT）. The calculated results are in good agreement with the available experimental data and other theoretical results. Through the quasi-harmonic Debye model, the dependences of the normalized lattice parameters a/ao and c/c0, axial ratio c/a, normalized primitive-cell volume V/Vo, Debye temperature θD and heat capacity Cv on pressure P and temperature T are obtained. It is found that the interlayer covalent interactions （Al-N bonds） are more （even a little） sensitive to temperature and pressure than intralayer ones （N-N bonds）, which gives rise to a little lattice anisotropy in the w-AlN.展开更多
This paper carries out first principles calculation of the structure, electronic and optical properties of BexZn1-xO alloys based on the density-functional theory for the compositions x = 0.0, 0.25, 0.5, 0.75, 1.0. Th...This paper carries out first principles calculation of the structure, electronic and optical properties of BexZn1-xO alloys based on the density-functional theory for the compositions x = 0.0, 0.25, 0.5, 0.75, 1.0. The lattice constants deviations of alloys obey Vegard＇s law well. The BexZn1-xO alloys have the direct band gap （Г-Г） character, and the bowing coefficients axe less than the available theoretical values. Moreover, it investigates in detail the optical properties （dielectric functions, absorption spectrum and refractive index） of these ternary mixed crystals. The obtained results agree well with the available theoretical and experimental values.展开更多
This paper carries out the First principles calculation of the crystal structures （zinc blende （B3） and rocksalt （B1）） and phase transition of boron arsenic （BAs） based on the density-functional theory. Using ...This paper carries out the First principles calculation of the crystal structures （zinc blende （B3） and rocksalt （B1）） and phase transition of boron arsenic （BAs） based on the density-functional theory. Using the relation between enthalpy and pressure, it finds that the transition phase from the B3 structural to the B] structural occurs at the pressure of l13.42GPa. Then the elastic constants Cll, C12, C44, bulk modulus, shear modulus, Young modulus, anisotropy factor, Kleinman parameter and Poisson ratio are discussed in detail for two polymorphs of BAs. The results of the structural parameters and elastic properties in B3 structure are in good agreement with the available theoretical and experimental values.展开更多
The phase transitions of semiconductor CaN from the Wurtzite （WZ） structure and the zinc-blende （ZB） structure to the rocksalt （R,S） structure are investigated by using the first-principles plane-wave pseudopote...The phase transitions of semiconductor CaN from the Wurtzite （WZ） structure and the zinc-blende （ZB） structure to the rocksalt （R,S） structure are investigated by using the first-principles plane-wave pseudopotential density functional method combined with the ultrasoft pseudopotentied scheme in the generalized gradient approximation （GGA） correction. It is found that the phase transitions from the WZ structure and the ZB structure to the R,S structure occur at pressures of 46.1 GPa and 45.2 GPa, respectively. The lattice parameters, bulk moduli and their pressure derivatives of these structures of CaN are also calculated. Our results are consistent with available experimental and other theoretical results. The dependence of the normalized formula-unit volume V/V0 on pressure P is also successfully obtained.展开更多
We investigate the electronic structure of Ag2HgSnSe4 in a wurtzite-stannite structure with the first principles method. This crystal is a direct band-gap compound. In addition the dielectric function, absorption coef...We investigate the electronic structure of Ag2HgSnSe4 in a wurtzite-stannite structure with the first principles method. This crystal is a direct band-gap compound. In addition the dielectric function, absorption coefficient, reflectivity, and energy-loss function are studied using the density functional theory in the generalized gradient approximation. We discuss the optical transitions between the valence bands and the conduction bands in the spectrum of the imaginary part of the dielectric function at length. We also find a very high absorption coefficient and a wide absorption band for this material. The prominent structures in the spectra of reflectivity and the energy-loss function are discussed in detail.展开更多
Density functional theory based calculations have been carried out to study structural, electronic, and magnetic properties of Znl-xCoxO （x = 0, 0.25, 0.50, 0.75） in the zinc-blende phase, and the generalized gradie...Density functional theory based calculations have been carried out to study structural, electronic, and magnetic properties of Znl-xCoxO （x = 0, 0.25, 0.50, 0.75） in the zinc-blende phase, and the generalized gradient approximation proposed by Wu and Cohen has been used. Our calculated lattice constants decrease while the bulk moduli increase with the increase of Co2＋ concentration. The calculated spin polarized band structures show the metallic behavior of Co-doped ZnO for both the up and the down spin cases with various doping concentrations. Moreover, the electron population is found to shift from the Zn-O bond to the Co-O bond with the increase of Co2~ concentration. The total magnetic moment~ the interstitial magnetic moment, the valence and the conduction band edge spin splitting energies, and the exchange constants decrease, while the local magnetic moments of Zn, Co, O, the exchange spin splitting energies, and crystal field splitting energies increase with the increase of dopant concentration.展开更多
文摘The electronic and optical properties of TiS2 are studied of density functional theory. A linearized and augmented by using an ab-initio calculation within the frame plane wave basis set with the generalized gradient approximation as proposed by Perdew et al. is used for the energy exchange-correlation determination. The results show a metallic character of TiS2, and the plots of total and partial densities of states of TiS2 show the metallic character of the bonds and a strong hybridization between the states d of Ti and p of S below the Fermi energy. The optical properties of the material such as real and imaginary parts of dielectric constant （ε（w） = ε1（w） ＋ iε2（w））, refractive index n（w）, optical reflectivity R（w）, for E / /x and E / /z are performed for the energy range of 0-.14 eV.
文摘The electronic band structures of wurtzite GaN with Ga and N vacancy defects are investigated by means of the first-principles total energy calculations in the neutral charge state. Our results show that the band structures can be significantly modified by the Ga and N vacancies in the GaN samples. Generally, the width of the valence band is reduced and the band gap is enlarged. The defect-induced bands can be introduced in the band gap of GMV due to the Ga and N vacancies. Moreover, the GaN with high density of N vacancies becomes an indirect gap semiconductor. Three defect bands due to Ga vacancy defects are created within the band gap and near the top of the valence band. In contrast, the N vacancies introduce four defect bands within the band gap. One is in the vicinity of the top of the valence band, and the others are near the bottom of the conduction band. The physical origin of the defect bands and modification of the band structures due to the Ga and N vacancies are analysed in depth.
文摘The structural and electronic properties of sodium bromide （NaBr） are investigated by the density functional theory （DFT） within the generalized gradient approximation （GGA） for the exchange and correlation energy. The equilibrium lattice constant, bulk modulus and its pressure derivative are obtained by fitting the calculated total energy to the third-order Birch-Murnaghan equation of state. The band structure along the higher symmetry axes in the Brillouin zone, the density of states （DOS） and the partial density of states （PDOS） are presented. The results have been discussed and compared with the available experimental and theoretical data.
基金Supported by the National Natural Science Foundation of China under Grant No 10174039, the Natural Science Foundation of Jiangsu Province under Grant No BK2002099, and the Science Foundation of Nanjing University of Science and Technology under Grant No AB96129.
文摘Hybrid density functional theory （DFT） calculations are performed to study MC2 （M= V, Cr, Fe and Co） clusters in the neutral and anionic charge states. We find that the equilibrium geometries of MC2 and their anions are all cyclic structures with C2v symmetry, which agrees well with the previous theoretical studies. The Mulliken charge and spin populations of MC2 clusters and their anions are also calculated, and it is found that the electron charge transformations from anions to neutral molecules mainly take place on the M atoms. Time-dependent DFT is used to calculate the excited states, and a theoretical assignment for the features in the experimental photoelectron spectrum is given, which are in good agreement with the available experimental data.
基金Project supported by the National Natural Science Foundation of China （Grant No 10576020）.
文摘The lattice parameter, bulk modulus and its pressure derivative of the wurtzite-type aluminium nitride （w-AlN） are investigated by using the Cambridge Serial Total Energy Package （CASTEP） program in the framework of Density Functional Theory （DFT）. The calculated results are in good agreement with the available experimental data and other theoretical results. Through the quasi-harmonic Debye model, the dependences of the normalized lattice parameters a/ao and c/c0, axial ratio c/a, normalized primitive-cell volume V/Vo, Debye temperature θD and heat capacity Cv on pressure P and temperature T are obtained. It is found that the interlayer covalent interactions （Al-N bonds） are more （even a little） sensitive to temperature and pressure than intralayer ones （N-N bonds）, which gives rise to a little lattice anisotropy in the w-AlN.
基金supported by the National Natural Science Foundation of China (Grant Nos. 10974139 and 10964002)the Specialized Research Fund for the Doctoral Program of Higher Education of China (Grant No. 20050610010)+1 种基金the Science-Technology Foundation of Guizhou Province of China (Grant Nos. [2009]2066,[2009]06 and [2010]2146)the Project of Aiding Elites’ Research Condition of Guizhou Province of China (Grant No. TZJF-2008-42)
文摘This paper carries out first principles calculation of the structure, electronic and optical properties of BexZn1-xO alloys based on the density-functional theory for the compositions x = 0.0, 0.25, 0.5, 0.75, 1.0. The lattice constants deviations of alloys obey Vegard＇s law well. The BexZn1-xO alloys have the direct band gap （Г-Г） character, and the bowing coefficients axe less than the available theoretical values. Moreover, it investigates in detail the optical properties （dielectric functions, absorption spectrum and refractive index） of these ternary mixed crystals. The obtained results agree well with the available theoretical and experimental values.
基金supported by the National Natural Science Foundation of China (Grant Nos. 10974139 and 10964002)the Specialized Research Fund for the Doctoral Program of Higher Education of China (Grant No. 20050610010)+1 种基金the Science-Technology Foundation of Guizhou Province of China (Grant Nos. [2009]2066 and [2009]06)the project of Aiding Elites’ Research Condition of Guizhou Province of China (Grant No. TZJF-2008-42)
文摘This paper carries out the First principles calculation of the crystal structures （zinc blende （B3） and rocksalt （B1）） and phase transition of boron arsenic （BAs） based on the density-functional theory. Using the relation between enthalpy and pressure, it finds that the transition phase from the B3 structural to the B] structural occurs at the pressure of l13.42GPa. Then the elastic constants Cll, C12, C44, bulk modulus, shear modulus, Young modulus, anisotropy factor, Kleinman parameter and Poisson ratio are discussed in detail for two polymorphs of BAs. The results of the structural parameters and elastic properties in B3 structure are in good agreement with the available theoretical and experimental values.
基金Project supported by the National Natural Science Foundation of China （Grant No 10576020）.
文摘The phase transitions of semiconductor CaN from the Wurtzite （WZ） structure and the zinc-blende （ZB） structure to the rocksalt （R,S） structure are investigated by using the first-principles plane-wave pseudopotential density functional method combined with the ultrasoft pseudopotentied scheme in the generalized gradient approximation （GGA） correction. It is found that the phase transitions from the WZ structure and the ZB structure to the R,S structure occur at pressures of 46.1 GPa and 45.2 GPa, respectively. The lattice parameters, bulk moduli and their pressure derivatives of these structures of CaN are also calculated. Our results are consistent with available experimental and other theoretical results. The dependence of the normalized formula-unit volume V/V0 on pressure P is also successfully obtained.
基金supported by the National Natural Science Foundation of China (Grant No. 10902029)
文摘We investigate the electronic structure of Ag2HgSnSe4 in a wurtzite-stannite structure with the first principles method. This crystal is a direct band-gap compound. In addition the dielectric function, absorption coefficient, reflectivity, and energy-loss function are studied using the density functional theory in the generalized gradient approximation. We discuss the optical transitions between the valence bands and the conduction bands in the spectrum of the imaginary part of the dielectric function at length. We also find a very high absorption coefficient and a wide absorption band for this material. The prominent structures in the spectra of reflectivity and the energy-loss function are discussed in detail.
基金Project supported by the Ministry of Higher Education (MOHE) of Malaysia and the Universiti Teknologi Malaysia (UTM)(Grant Nos. Q.J13000.7126.00J33, R.J130000.7726.4D034, and R.J130000.7826.4F113)
文摘Density functional theory based calculations have been carried out to study structural, electronic, and magnetic properties of Znl-xCoxO （x = 0, 0.25, 0.50, 0.75） in the zinc-blende phase, and the generalized gradient approximation proposed by Wu and Cohen has been used. Our calculated lattice constants decrease while the bulk moduli increase with the increase of Co2＋ concentration. The calculated spin polarized band structures show the metallic behavior of Co-doped ZnO for both the up and the down spin cases with various doping concentrations. Moreover, the electron population is found to shift from the Zn-O bond to the Co-O bond with the increase of Co2~ concentration. The total magnetic moment~ the interstitial magnetic moment, the valence and the conduction band edge spin splitting energies, and the exchange constants decrease, while the local magnetic moments of Zn, Co, O, the exchange spin splitting energies, and crystal field splitting energies increase with the increase of dopant concentration.
