The structural stability, thermodynamic and optical properties of delafossite CuAlO2 were investigated using the norm-conserving pseudopotential technique based on the fi rst-principle density-functional theory. The g...The structural stability, thermodynamic and optical properties of delafossite CuAlO2 were investigated using the norm-conserving pseudopotential technique based on the fi rst-principle density-functional theory. The ground-state properties obtained by minimizing the total energy were in favorable agreement with previous works. By using the quasi-harmonic Debye model, the thermodynamic properties including the Debye temperature QD, heat capacity CV, thermal expansion coeffi cient a, and Grüneisen parameter g were successfully obtained in the temperature range from 0 to 1 000 K and pressure range from 0 to 80 GPa, respectively. The optical properties including dielectric function e（v）, absorption coeffi cient a（v）, refl ectivity coeffi cient R（v）, and refractive index n（v） were also calculated and analyzed.展开更多
The band structures,density of states,phonon,optical properties,and thermodynamic properties of β-La_2S_3 were calculated from first-principles using the plane-wave pseudopotential method.First,the structures were fu...The band structures,density of states,phonon,optical properties,and thermodynamic properties of β-La_2S_3 were calculated from first-principles using the plane-wave pseudopotential method.First,the structures were fully relaxed through the first-principles method.Then,the zone-center phonon-mode frequencies were evaluated within the framework of density functional perturbation theory.Properties related to the structure,phonons,optics,elastic constants,and thermodynamics of β-La_2S_3 were reported.The dielectric function,refractive index,absorption coefficient,extinction coefficient,infrared（IR） reflectance,energy,heat capacity,and Debye temperature spectra were also given β-La_2S_3 was a direct-gap semiconductor,and calculation indicated that its energy gap was 0.191 eV.From the phonon spectra,it could be concluded that the lattice dynamics were stable.A strong IR reflection occurred in a range of 0-1000 nm,arising from several strong IR-active modes,resulting in poor transmission properties.Relatively good transmission properties were observed in the range above 2000 nm,with low reflectivity and dissipation due to the absence of IR-active or weak modes.展开更多
In the present computational study,we found that Er:Lu_(2)O_(3)materials have promise for application in laser applications.The crystal structure and the electronic and optical properties of Er:Lu_(2)O_(3)materials we...In the present computational study,we found that Er:Lu_(2)O_(3)materials have promise for application in laser applications.The crystal structure and the electronic and optical properties of Er:Lu_(2)O_(3)materials were studied using first-principle calculations under the framework of density functional theory.Based on the experimental and calculated results,the structure of Lu_(2)O_(3)was established.The calculated results show that doping by Er^(3+)can effectively improve its absorption coefficient in the ultraviolet region and improve the static dielectric constant of Lu_(2)O_(3).As the doping concentration of Er^(3+)increases,the energy of the valence band electrons excited to the conduction band decreases,and the transition is more likely to occur.The absorption coefficient,reflectance,and electron energy loss spectroscopy are bathochromic shifted.The Lu_(2-x)Er_(x)O_(3)(0<x<0.09375)system still retains a low absorption coefficient reflectance in the mid-infrared and visible regions.Our calculations therefore show that rare earth doping can effectively regulate the electronic structure and optical properties of Lu_(2)O_(3).展开更多
The electronic structure and optical properties of CdGeAs2 were calculated by the first principle method using ultra-soft pseudo-potential approach of the plane wave based upon density functional theory （DFT）. Mulli...The electronic structure and optical properties of CdGeAs2 were calculated by the first principle method using ultra-soft pseudo-potential approach of the plane wave based upon density functional theory （DFT）. Mulliken population analysis showed that atomic orbital hybridization occurs when forming chemical bonds. The relationship between inter-band transition and optical properties was analyzed to provide a theoretical basis for investigating or controlling CdGeAs2 crystal defects.展开更多
The systematic trends of electrionic structure and optical properties of rutile （P42/mnm） RuO2 have been cal- culated by using the plane-wave norm-conserving pseudopotential density functional theory （DFT） method ...The systematic trends of electrionic structure and optical properties of rutile （P42/mnm） RuO2 have been cal- culated by using the plane-wave norm-conserving pseudopotential density functional theory （DFT） method within the generalised gradient approximation （GGA） for the exchange-correlation potential. The obtained equilibrium structure parameters are in excellent agreement with the experimental data. The calculated bulk modulus and elastic constants are also in good agreement with the experimental data and available theoretical calculations. Analysis based on elec- tronic structure and pseudogap reveals that the bonding nature in RuO2 is a combination of covalent, ionic and metallic bonds. Based on a Kramers Kronig analysis of the reflectivity, we have obtained the spectral dependence of the real and imaginary parts of the complex dielectric constant （~1 and z2, respectively） and the refractive index （n）; and comparisons have shown that the theoretical results agree well with the experimental data as well. Meanwhile, we have also calculated the absorption coefficient, reflectivity index, electron energy loss function of RuO2 for radiation up to 30 eV. As a result, the predicted reflectivity index is in good agreement with the experimental data at low energies.展开更多
The structural, elastic, and thermodynamic properties of cubic-Fe2TiA1 under high temperatures and pressures are investigated by performing ab initio calculation and using the quasi-harmonic Debye model. Some ground s...The structural, elastic, and thermodynamic properties of cubic-Fe2TiA1 under high temperatures and pressures are investigated by performing ab initio calculation and using the quasi-harmonic Debye model. Some ground state properties such as lattice constant, bulk modulus, pressure derivative of the bulk modulus, and elastic constants are in good agreement with the available experimental results and theoretical data. The thermodynamic properties of Fe2TiA1 such as thermal expansion coefficient, Debye temperature, and heat capacity in ranges of 0 K-1200 K and 0 GPa-250 GPa are also obtained. The calculation results indicate that the heat capacities at different pressures all increase with temperature increasing and are close to the Dulong-Petit limit at higher temperatures, Debye temperature decreases with temperature increasing, and increases with pressure rising. The cubic-FezTiA1 is stable mechanically under 250 GPa. Moreover, under lower pressure, thermal expansion coefficient rises rapidly with temperature increasing, and the increasing rate becomes slow at higher pressure.展开更多
Density functional calculations were used to investigate the structural,electronic,optical and thermal properties of Cr_4AlB_6.The optimized lattice constants and atomic positions accord well with the experimental dat...Density functional calculations were used to investigate the structural,electronic,optical and thermal properties of Cr_4AlB_6.The optimized lattice constants and atomic positions accord well with the experimental data.The analysis of band structure and density of states confirms the metallic nature of Cr_4AlB_6.The static dielectric constant e1（0） is about 128.0,and the maximum optical conductivity occurs at about 8.12 eV.In the photon energy range from 7.87 to 23.48 e V,Cr_4AlB_6 presents a metal reflective property.The plasma resonance frequency wp of Cr_4AlB_6 is at the photon energy of 23.85 eV,and Cr_4AlB_6 will be transparent and change from metallic to dielectric response if the incident light has frequency greater than the plasma frequency of Cr_4AlB_6.Thermodynamic properties including the primitive cell volume and thermal expansion,the bulk modulus and heat capacity Cv were further investigated with the increasing temperature and pressure by using the quasi-harmonic Debye model.展开更多
We investigate the elastic and the thermodynamic properties of nanolaminate V2GeC by using the ab initio pseudopotential total energy method. The axial compressibility shows that the c axis is always stiffer than the ...We investigate the elastic and the thermodynamic properties of nanolaminate V2GeC by using the ab initio pseudopotential total energy method. The axial compressibility shows that the c axis is always stiffer than the a axis. The elastic constant calculations demonstrate that the structural stability is within 0-800 GPa. The calculations of Young＇s and shear moduli reveal the softening behaviour at about 300 GPa. The Possion ratio makes a higher ionic or a weaker covalent contribution to intra-atomic bonding and the degree of ionicity increases with pressure. The relationship between brittleness and ductility shows that V2GeC is brittle in ambient conditions and the brittleness decreases and ductility increases with pressure. Moveover, we find that V2CeC is largely isotropic in compression and in shear, and the degree of isotropy decreases with pressure. The Griineisen parameter, the Debye temperature and the thermal expansion coefficient are also successfully obtained for the first time.展开更多
The electronic structure and the optical properties of Ca<sub>2</sub>Ge have been calculated by the first-principles pseudo potential method. The results of the electric structure show that Ca<sub>2&...The electronic structure and the optical properties of Ca<sub>2</sub>Ge have been calculated by the first-principles pseudo potential method. The results of the electric structure show that Ca<sub>2</sub>Ge bulk is a direct semiconductor with the band gap of 0.306 eV, the conduction band is mainly composed of Ca 3d, the valence bands is mainly composed of Ge 3p. With Sr-doping, Ca<sub>2</sub>Ge bulk is a direct semiconductor with the band gap of 0.350 eV, the conduction bands are mainly composed of Ca 3d and Sr 3d, the valence bands are mainly composed of Ge 3p and Sr 3d. The results of the optical properties show that the dielectric constant of Ca<sub>2</sub>Ge bulk is reduced from 21.52 to 13.94, the reflectivity is decreased, and the absorption is increased with Sr-doping. The optical properties are improved with Sr-doping, the results offer theoretical guide for the optical properties control of Ca<sub>2</sub>Ge.展开更多
The electronic structures,chemical bonding,elastic and optical properties of the ternary stannide phase Na2MgSn were investigated by using density-fimctional theory（DFT） within generalized gradient approximation（GG...The electronic structures,chemical bonding,elastic and optical properties of the ternary stannide phase Na2MgSn were investigated by using density-fimctional theory（DFT） within generalized gradient approximation（GGA）.The calculated energy band structures show that Na2MgSn is an indirect semiconductor material with a narrow band gap 0.126 eV.The density of state（DOS）and the partial density of state（PDOS） calculations show that the DOS near the Fermi level is mainly from the Na 2p,Mg 3p and Sn5 p states.Population analysis suggests that there are strongly bonded Mg-Sn honeycomb layers in Na2MgSn.Basic physical properties,such as lattice constant,bulk modulus,shear modulus,elastic constants c（ij） were calculated.The elastic modulus E and Poisson ratio v were also predicted.The results show that Na2MgSn is mechanically stable soft material and behaves in a brittle manner.Detailed analysis of all optical functions reveals that Na2MgSn is a better dielectric material,and reflectivity spectra show that Na2MgSn promise as good coating materials in the energy regions 6.24-10.49 eV.展开更多
The structural, electronic, optical and thermodynamic properties of Mo2Ga2C are investigated using density func- tional theory （DFT） within the generalized gradient approximation （GGA）. The optimized crystal struc...The structural, electronic, optical and thermodynamic properties of Mo2Ga2C are investigated using density func- tional theory （DFT） within the generalized gradient approximation （GGA）. The optimized crystal structure is obtained and the lattice parameters are compared with available experimental data. The electronic density of states （DOS） is calculated and analyzed. The metallic behavior for the compound is confirmed and the value of DOS at Fermi level is 4.2 states per unit cell per eV. Technologically important optical parameters （e.g., dielectric function, refractive index, absorption coefficient, photo conductivity, reflectivity, and loss function） are calculated for the first time. The study of dielectric constant （ε1） indicates the Drude-like behavior. The absorption and conductivity spectra suggest that the compound is metallic. The reflectance spectrum shows that this compound has the potential to be used as a solar reflector. The thermodynamic properties such as the temperature and pressure dependent bulk modulus, Debye temperature, specific heats, and thermal expansion coefficient of Mo2Ga2C MAX phase are derived from the quasi-harmonic Debye model with phononic effect also for the first time. Analysis of Tc expression using available parameter values （DOS, Debye temperature, atomic mass, etc.） suggests that the compound is less likely to be superconductor.展开更多
Using the first principle methods based on the plane-wave pseudo-potential theory, band structure, density of states and optical properties of CrSi2 were studied. The calculation of band structure shows that CrSi2 is ...Using the first principle methods based on the plane-wave pseudo-potential theory, band structure, density of states and optical properties of CrSi2 were studied. The calculation of band structure shows that CrSi2 is an indirect semiconductor whose band gap is 0.353 eV. Density of states is mainly composed of 3d electron of Cr and 3p electron of Si. Dielectric function, refractive index, reflectivity, and absorption coefficient of CrSi2 are also calculated. The calculation results of optical properties are in agreement with the experiments.展开更多
The electronic structure,densities of states and optical properties of the stable orthorhombic BaSi2 have been calculated using the first-principle density function theory and pseudopotential method. The results show ...The electronic structure,densities of states and optical properties of the stable orthorhombic BaSi2 have been calculated using the first-principle density function theory and pseudopotential method. The results show that BaSi2 is an indirect semiconductor with the band gap of 1.086 eV,the valence bands of BaSi2 are mainly composed of Si 3p,3s and Ba 5d,and the conduction bands are mainly composed of Ba 6s,5d as well as Si 3p. The static dielectric function ε1(0) is 11.17,the reflectivity n0 is 3.35,and the biggest peak of the absorption coefficient is 2.15×105 cm-1.展开更多
The diamond anvil cell experiments have revealed that the calcium ferrite(CF)-type aluminous phase is probably an important component of subducted mid-oceanic ridge basalt(MORB) in the lower mantle. In this study, we ...The diamond anvil cell experiments have revealed that the calcium ferrite(CF)-type aluminous phase is probably an important component of subducted mid-oceanic ridge basalt(MORB) in the lower mantle. In this study, we have performed first principles lattice dynamics calculations for the Mg Al_2O_4 end-member of the aluminous phase based on density functional perturbation theory using two functionals within the local density approximation(LDA) and generalized gradient approximation(GGA) for bracketing the calculated properties at their lower and upper limits, respectively. A simple empirical pressure correction at zero temperature has been applied to both LDA and GGA. The results of room-temperature equation of state(EOS) and zero-pressure thermal expansion calculated by GGA with pressure correction have shown the best agreement with available experimental data. The high-pressure and temperature thermodynamic properties have been obtained using the GGA with correction method. The pressure-volume relations are fitted with a third-order high-temperature Birch-Murnaghan EOS. The isobaric heat capacity, the coefficient of thermal expansion and isothermal bulk modulus are fitted with polynomials and their coefficients are reported in the range of 0–40 GPa and 300–2000 K. The density profile of MORB estimated using the computational thermo-elastic constants supports the hypothesis that the subducted oceanic slabs could gain enough downwelling forces into the lower mantle.展开更多
基金Funded by the National Natural Science Foundation of China(Nos.11204192 and 11104099)the National Key Laboratory Fund for Shock Wave and Detonation Physics Research of the China Academy of Engineering Physics(No.9140C671101110C6709)+1 种基金the Defense Industrial Technology Development Program of China(No.B1520110002)the National Basic Research Program of China(No.2010CB731600)
文摘The structural stability, thermodynamic and optical properties of delafossite CuAlO2 were investigated using the norm-conserving pseudopotential technique based on the fi rst-principle density-functional theory. The ground-state properties obtained by minimizing the total energy were in favorable agreement with previous works. By using the quasi-harmonic Debye model, the thermodynamic properties including the Debye temperature QD, heat capacity CV, thermal expansion coeffi cient a, and Grüneisen parameter g were successfully obtained in the temperature range from 0 to 1 000 K and pressure range from 0 to 80 GPa, respectively. The optical properties including dielectric function e（v）, absorption coeffi cient a（v）, refl ectivity coeffi cient R（v）, and refractive index n（v） were also calculated and analyzed.
基金supported by National Natural Science Foundation of China(51372203,51332004,51571166,11304238)
文摘The band structures,density of states,phonon,optical properties,and thermodynamic properties of β-La_2S_3 were calculated from first-principles using the plane-wave pseudopotential method.First,the structures were fully relaxed through the first-principles method.Then,the zone-center phonon-mode frequencies were evaluated within the framework of density functional perturbation theory.Properties related to the structure,phonons,optics,elastic constants,and thermodynamics of β-La_2S_3 were reported.The dielectric function,refractive index,absorption coefficient,extinction coefficient,infrared（IR） reflectance,energy,heat capacity,and Debye temperature spectra were also given β-La_2S_3 was a direct-gap semiconductor,and calculation indicated that its energy gap was 0.191 eV.From the phonon spectra,it could be concluded that the lattice dynamics were stable.A strong IR reflection occurred in a range of 0-1000 nm,arising from several strong IR-active modes,resulting in poor transmission properties.Relatively good transmission properties were observed in the range above 2000 nm,with low reflectivity and dissipation due to the absence of IR-active or weak modes.
基金Project support by the National Natural Science Foundation of China(51372203.51332004,51571166).
文摘In the present computational study,we found that Er:Lu_(2)O_(3)materials have promise for application in laser applications.The crystal structure and the electronic and optical properties of Er:Lu_(2)O_(3)materials were studied using first-principle calculations under the framework of density functional theory.Based on the experimental and calculated results,the structure of Lu_(2)O_(3)was established.The calculated results show that doping by Er^(3+)can effectively improve its absorption coefficient in the ultraviolet region and improve the static dielectric constant of Lu_(2)O_(3).As the doping concentration of Er^(3+)increases,the energy of the valence band electrons excited to the conduction band decreases,and the transition is more likely to occur.The absorption coefficient,reflectance,and electron energy loss spectroscopy are bathochromic shifted.The Lu_(2-x)Er_(x)O_(3)(0<x<0.09375)system still retains a low absorption coefficient reflectance in the mid-infrared and visible regions.Our calculations therefore show that rare earth doping can effectively regulate the electronic structure and optical properties of Lu_(2)O_(3).
基金supported by the National Natural Science Foundation of China (E5057201)Heilongjiang Provincial Scientific and Technological Projects
文摘The electronic structure and optical properties of CdGeAs2 were calculated by the first principle method using ultra-soft pseudo-potential approach of the plane wave based upon density functional theory （DFT）. Mulliken population analysis showed that atomic orbital hybridization occurs when forming chemical bonds. The relationship between inter-band transition and optical properties was analyzed to provide a theoretical basis for investigating or controlling CdGeAs2 crystal defects.
基金supported by the China Scholarship Council (CSC) and the National Natural Science Foundation of China (Grant Nos. 10676025 and 10574096)the Science-Technology Foundation for Young Scientist of Sichuan Province,China (Grant No. 09ZQ026-049)
文摘The systematic trends of electrionic structure and optical properties of rutile （P42/mnm） RuO2 have been cal- culated by using the plane-wave norm-conserving pseudopotential density functional theory （DFT） method within the generalised gradient approximation （GGA） for the exchange-correlation potential. The obtained equilibrium structure parameters are in excellent agreement with the experimental data. The calculated bulk modulus and elastic constants are also in good agreement with the experimental data and available theoretical calculations. Analysis based on elec- tronic structure and pseudogap reveals that the bonding nature in RuO2 is a combination of covalent, ionic and metallic bonds. Based on a Kramers Kronig analysis of the reflectivity, we have obtained the spectral dependence of the real and imaginary parts of the complex dielectric constant （~1 and z2, respectively） and the refractive index （n）; and comparisons have shown that the theoretical results agree well with the experimental data as well. Meanwhile, we have also calculated the absorption coefficient, reflectivity index, electron energy loss function of RuO2 for radiation up to 30 eV. As a result, the predicted reflectivity index is in good agreement with the experimental data at low energies.
基金supported by the Advanced Research Foundation,China(Grant No.20100210)
文摘The structural, elastic, and thermodynamic properties of cubic-Fe2TiA1 under high temperatures and pressures are investigated by performing ab initio calculation and using the quasi-harmonic Debye model. Some ground state properties such as lattice constant, bulk modulus, pressure derivative of the bulk modulus, and elastic constants are in good agreement with the available experimental results and theoretical data. The thermodynamic properties of Fe2TiA1 such as thermal expansion coefficient, Debye temperature, and heat capacity in ranges of 0 K-1200 K and 0 GPa-250 GPa are also obtained. The calculation results indicate that the heat capacities at different pressures all increase with temperature increasing and are close to the Dulong-Petit limit at higher temperatures, Debye temperature decreases with temperature increasing, and increases with pressure rising. The cubic-FezTiA1 is stable mechanically under 250 GPa. Moreover, under lower pressure, thermal expansion coefficient rises rapidly with temperature increasing, and the increasing rate becomes slow at higher pressure.
基金supported by the National Natural Science Foundation of China(No.U1304111)Program for Science&Technology Innovation Talents in Universities of Henan Province(No.14HASTIT039)the Innovation Team of Henan University of Science and Technology(2015XTD001)
文摘Density functional calculations were used to investigate the structural,electronic,optical and thermal properties of Cr_4AlB_6.The optimized lattice constants and atomic positions accord well with the experimental data.The analysis of band structure and density of states confirms the metallic nature of Cr_4AlB_6.The static dielectric constant e1（0） is about 128.0,and the maximum optical conductivity occurs at about 8.12 eV.In the photon energy range from 7.87 to 23.48 e V,Cr_4AlB_6 presents a metal reflective property.The plasma resonance frequency wp of Cr_4AlB_6 is at the photon energy of 23.85 eV,and Cr_4AlB_6 will be transparent and change from metallic to dielectric response if the incident light has frequency greater than the plasma frequency of Cr_4AlB_6.Thermodynamic properties including the primitive cell volume and thermal expansion,the bulk modulus and heat capacity Cv were further investigated with the increasing temperature and pressure by using the quasi-harmonic Debye model.
基金Project supported by the National Natural Science Foundation of China (Grant Nos. 10974139, 10964002 and 11104247)the Natural Science Foundation of Guizhou Province, China (Grant No. [2009]2066)+1 种基金the Project of Aiding Elites' Research Condition of Guizhou Province, China (Grant No. TZJF-2008-42)the Science Foundation from Education Ministry of Zhejiang Province,China (Grant No. Y201121807)
文摘We investigate the elastic and the thermodynamic properties of nanolaminate V2GeC by using the ab initio pseudopotential total energy method. The axial compressibility shows that the c axis is always stiffer than the a axis. The elastic constant calculations demonstrate that the structural stability is within 0-800 GPa. The calculations of Young＇s and shear moduli reveal the softening behaviour at about 300 GPa. The Possion ratio makes a higher ionic or a weaker covalent contribution to intra-atomic bonding and the degree of ionicity increases with pressure. The relationship between brittleness and ductility shows that V2GeC is brittle in ambient conditions and the brittleness decreases and ductility increases with pressure. Moveover, we find that V2CeC is largely isotropic in compression and in shear, and the degree of isotropy decreases with pressure. The Griineisen parameter, the Debye temperature and the thermal expansion coefficient are also successfully obtained for the first time.
文摘The electronic structure and the optical properties of Ca<sub>2</sub>Ge have been calculated by the first-principles pseudo potential method. The results of the electric structure show that Ca<sub>2</sub>Ge bulk is a direct semiconductor with the band gap of 0.306 eV, the conduction band is mainly composed of Ca 3d, the valence bands is mainly composed of Ge 3p. With Sr-doping, Ca<sub>2</sub>Ge bulk is a direct semiconductor with the band gap of 0.350 eV, the conduction bands are mainly composed of Ca 3d and Sr 3d, the valence bands are mainly composed of Ge 3p and Sr 3d. The results of the optical properties show that the dielectric constant of Ca<sub>2</sub>Ge bulk is reduced from 21.52 to 13.94, the reflectivity is decreased, and the absorption is increased with Sr-doping. The optical properties are improved with Sr-doping, the results offer theoretical guide for the optical properties control of Ca<sub>2</sub>Ge.
基金Project (11271121) supported by the National Natural Science Foundation of ChinaProject (11JJ2002) supported by the Natural Science Foundation of Hunan Province,China+1 种基金Project (11K038) supported by Key Laboratory of High Performance Computing and Stochastic Information Processing of Ministry of Education of ChinaProjects (2013GK3130,2014GK3090) supported by the Scientific and Techrnological Plan of Hunan Province,China
文摘The electronic structures,chemical bonding,elastic and optical properties of the ternary stannide phase Na2MgSn were investigated by using density-fimctional theory（DFT） within generalized gradient approximation（GGA）.The calculated energy band structures show that Na2MgSn is an indirect semiconductor material with a narrow band gap 0.126 eV.The density of state（DOS）and the partial density of state（PDOS） calculations show that the DOS near the Fermi level is mainly from the Na 2p,Mg 3p and Sn5 p states.Population analysis suggests that there are strongly bonded Mg-Sn honeycomb layers in Na2MgSn.Basic physical properties,such as lattice constant,bulk modulus,shear modulus,elastic constants c（ij） were calculated.The elastic modulus E and Poisson ratio v were also predicted.The results show that Na2MgSn is mechanically stable soft material and behaves in a brittle manner.Detailed analysis of all optical functions reveals that Na2MgSn is a better dielectric material,and reflectivity spectra show that Na2MgSn promise as good coating materials in the energy regions 6.24-10.49 eV.
文摘The structural, electronic, optical and thermodynamic properties of Mo2Ga2C are investigated using density func- tional theory （DFT） within the generalized gradient approximation （GGA）. The optimized crystal structure is obtained and the lattice parameters are compared with available experimental data. The electronic density of states （DOS） is calculated and analyzed. The metallic behavior for the compound is confirmed and the value of DOS at Fermi level is 4.2 states per unit cell per eV. Technologically important optical parameters （e.g., dielectric function, refractive index, absorption coefficient, photo conductivity, reflectivity, and loss function） are calculated for the first time. The study of dielectric constant （ε1） indicates the Drude-like behavior. The absorption and conductivity spectra suggest that the compound is metallic. The reflectance spectrum shows that this compound has the potential to be used as a solar reflector. The thermodynamic properties such as the temperature and pressure dependent bulk modulus, Debye temperature, specific heats, and thermal expansion coefficient of Mo2Ga2C MAX phase are derived from the quasi-harmonic Debye model with phononic effect also for the first time. Analysis of Tc expression using available parameter values （DOS, Debye temperature, atomic mass, etc.） suggests that the compound is less likely to be superconductor.
基金Supported by the National Natural Science Foundation of China (Grant No.60566001)the Specialized Research Fund for the Doctoral Program of Higher Education of China (Grant No.20050657003)+4 种基金the Scientific Research Foundation for the Returned Overseas Chinese Scholars, Ministry of Education of China (Grant No.(2005)383)the Program for Excellent Young Talents of Guizhou Province (No.20050528)the Specialized Nomarch Research Fund for the Excellent Science and Technology and Education Talent’s Projects of Guizhou Provincethe Scientific and Technological Projects for the Returned Overseas Chinese Scholars, Guizhou Province (Grant No.(2004)03)the Top Talent’s Scientific Research Project of Organization Department of Guizhou Province
文摘Using the first principle methods based on the plane-wave pseudo-potential theory, band structure, density of states and optical properties of CrSi2 were studied. The calculation of band structure shows that CrSi2 is an indirect semiconductor whose band gap is 0.353 eV. Density of states is mainly composed of 3d electron of Cr and 3p electron of Si. Dielectric function, refractive index, reflectivity, and absorption coefficient of CrSi2 are also calculated. The calculation results of optical properties are in agreement with the experiments.
基金Supported by the National Natural Science Foundation of China (Grant Nos. 60566001 and 60766002)the Specialized Research Fund for the Doctoral Program of Higher Education of China (Grant No. 20050657003)+3 种基金the Scientific Research Foundation for the Returned Overseas Chinese Scholars, Ministry of Education of China (Grant No. (2005)383)the Specialized Fund of Nomarch for Excellent Talent of Science and Technology of Guizhou Province (Grant No. Z053114)the Scientific and Technological Projects for the Returned Overseas of Guizhou Province (Grant No. (2004)03)the Top Talent's Scientific Research Project of Organization Department of Guizhou Province (Grant No. Z053123)
文摘The electronic structure,densities of states and optical properties of the stable orthorhombic BaSi2 have been calculated using the first-principle density function theory and pseudopotential method. The results show that BaSi2 is an indirect semiconductor with the band gap of 1.086 eV,the valence bands of BaSi2 are mainly composed of Si 3p,3s and Ba 5d,and the conduction bands are mainly composed of Ba 6s,5d as well as Si 3p. The static dielectric function ε1(0) is 11.17,the reflectivity n0 is 3.35,and the biggest peak of the absorption coefficient is 2.15×105 cm-1.
基金supported by the State Key Development Program of Basic Research of China(Grant No.2014CB845905)the National Natural Science Foundation of China(Grant Nos.41402033&40973003)the Fundamental Research Funds for the Central Universities(Grant No.20620140385)
文摘The diamond anvil cell experiments have revealed that the calcium ferrite(CF)-type aluminous phase is probably an important component of subducted mid-oceanic ridge basalt(MORB) in the lower mantle. In this study, we have performed first principles lattice dynamics calculations for the Mg Al_2O_4 end-member of the aluminous phase based on density functional perturbation theory using two functionals within the local density approximation(LDA) and generalized gradient approximation(GGA) for bracketing the calculated properties at their lower and upper limits, respectively. A simple empirical pressure correction at zero temperature has been applied to both LDA and GGA. The results of room-temperature equation of state(EOS) and zero-pressure thermal expansion calculated by GGA with pressure correction have shown the best agreement with available experimental data. The high-pressure and temperature thermodynamic properties have been obtained using the GGA with correction method. The pressure-volume relations are fitted with a third-order high-temperature Birch-Murnaghan EOS. The isobaric heat capacity, the coefficient of thermal expansion and isothermal bulk modulus are fitted with polynomials and their coefficients are reported in the range of 0–40 GPa and 300–2000 K. The density profile of MORB estimated using the computational thermo-elastic constants supports the hypothesis that the subducted oceanic slabs could gain enough downwelling forces into the lower mantle.
