Ab initio calculations are performed on the electronic, structural, elastic and optical properties of the cubic per- ovskite KCdF3. Tile Kohn Sham equations are solved by applying the full potential linearized augment...Ab initio calculations are performed on the electronic, structural, elastic and optical properties of the cubic per- ovskite KCdF3. Tile Kohn Sham equations are solved by applying the full potential linearized augmented plane wave （FP-LAPW） method. The exchange correlation effects are included through the local density approximation （LDA ）, generalized gradient approximation （GGA） and modified Becke-Johnson （mBJ） exchange potential The calculated lattice constant is in good agreement with the experimental result. The elastic properties such as elastic constants, anisotropy factor, shear modulus, Young＇s modulus and Poisson＇s ratio are calculated. KCdF3 is ductile and elastically anisotropic. The calculations of the electronic band structure, density of states （DOS） and charge density show that this compound has an indirect energy band gap （M-F） with a mixed ionic and covalent bonding. The contribution of the different bands is analyzed from the total and partial density of states curves. Optical response of the dielectric functions, optical reflectivity, absorption coefficient, real part of optical conductivity, refractive index, extinction coefficient and electron energy loss, are presented for the energy range of O-40eV. The compound KCdF3 can be used for high-frequency optical and optoelectronic devices.展开更多
Electronic structure and magnetic properties of wurtzite ZnO semiconductor doped with rare earth （RE=La, Ce, Pr, Pm, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm and Yb） atoms were studied using spin-polarized density functio...Electronic structure and magnetic properties of wurtzite ZnO semiconductor doped with rare earth （RE=La, Ce, Pr, Pm, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm and Yb） atoms were studied using spin-polarized density functional theory based on the full-potential linear augmented plane wave （FP-LAPW） method as implemented in the Wien2k code. In this approach the generalized gradient approximation （GGA） was used for the exchange-correlation （XC） potential. Our results showed that the substitution of RE ions in ZnO induced spins polarized localized states in the band gap. Moreover, the studied DMSs compounds retained half metallicity at dopant concentration x=0.625%for most of the studied elements, with 100%spin polarization at the Fermi level （EF）. The total magnetic moments of these compounds existed due to RE 4f states present at EF, while small induced magnetic moments existed on other non-magnetic atoms as well. Finally, the energy difference between far and near configurations was investigated. It was found that the room temperature ferromagnetism was possible for RE-doped ZnO at near configuration. Since the RE-RE separation was long enough （far configuration） for magnetic coupling, the system became paramagnetic or antiferromagnetic ground state.展开更多
The electronic structures of the titanium dioxide（TiO2） doped with V and Fe were analyzed by using first-principle calculations based on the density functional theory（DFT） with the full potential linearized augmen...The electronic structures of the titanium dioxide（TiO2） doped with V and Fe were analyzed by using first-principle calculations based on the density functional theory（DFT） with the full potential linearized augmented plane wave method （FP-LAPW）. The fully optimized structure and the relaxation introduced by impurity were obtained by minimizing the total energy and atomic forces. The unit cell of the V-doped anatase TiO2 is smaller than that of the non-doped one, but for the Fe-doped one, the case is just the opposite. It is found that the apical Ti-O and impurity-O bond lengths of the V/Fe-doped anatase TiO2 are greater than those of the non-doped structure, but smaller for the equatorial bond length. Through the band structures and the density of states, the V-doped TiO2 is shown to be a kind of half-metal, while the Fe-doped TiO2 a kind of metal. The magnetic moments of the V/Fe-doped system are mainly generated by the dopants. The results may be helpful for us to understand the experimental outcome of this system.展开更多
The mechanical, electronic and magnetic properties of non-magnetic MgTe and ferro-magnetic （FM） Mgo.75 TM025 Te （TM = Fe, Co, Ni） in the zinc-blende phase are studied by ab-initio calculations for the first time. ...The mechanical, electronic and magnetic properties of non-magnetic MgTe and ferro-magnetic （FM） Mgo.75 TM025 Te （TM = Fe, Co, Ni） in the zinc-blende phase are studied by ab-initio calculations for the first time. We use the generalized gradient approximation functional for computing the structural stability, and mechanical properties, while the modified Becke and Johnson local （spin） density approximation （mBJLDA） is utilized for determining the electronic and magnetic properties. By comparing the energies of non-magnetic and FM calculations, we find that the compounds are stable in the FM phase, which is confirmed by their structural stabilities in terms of enthalpy of formation. Detailed descriptions of elastic properties of Mgo.75TMo.25Te alloys in the FM phase are also presented. For electronic properties, the spin- polarized electronic band structures and density of states are computed, showing that these compounds are direct bandgap materials with strong hybridizations of TM 3d states and Te p states. Further, the ferromagnetism is discussed in terms of the Zener free electron model, RKKY model and double exchange model. The charge density contours in the （110） plane are calculated to study bonding properties. The spin exchange splitting and crystal field splitting energies are also calculated. The distribution of electron spin density is employed in computing the magnetic moments appearing at the magnetic sites （Fe, Co, Ni）, as well as at the non-magnetic sites （Mg, Te）. It is found that the p-d hybridization causes not only magnetic moments on the magnetic sites but also induces negligibly small magnetic moments at the non-magnetic sites.展开更多
Using the full potential linearized augmented plane wave FP-LAPW method within local density ap-proximation LDA, we have studied positron diffusion and surface emission in Cd-based semiconductors. This requires the ca...Using the full potential linearized augmented plane wave FP-LAPW method within local density ap-proximation LDA, we have studied positron diffusion and surface emission in Cd-based semiconductors. This requires the calculation of electron and positron band structures. In the absence of experimental and theoretical data for CdX (X=S,Se,Te) we have treated the Si, which has been studied by several authors, as a test case. Predictive results on positron effective masses, deformation potentials, positron work functions, diffusion constants and positron mobilities are presented for CdX (X=S, Se, Te). Our calculated data for Si are compared with experimental and recent theoretical results.展开更多
We report the electronic band structure and optical parameters of X-Phosphides （X=B, AI, Ga, In） by first-principles technique based on a new approximation known as modified Becke-Johnson （roB J）. This potential i...We report the electronic band structure and optical parameters of X-Phosphides （X=B, AI, Ga, In） by first-principles technique based on a new approximation known as modified Becke-Johnson （roB J）. This potential is considered more accurate in elaborating excited states properties of insulators and semiconductors as compared to LDA and GGA. The present calculated band gaps values of BP, AlP, GaP, and InP are 1.867 eV, 2.268 eV, 2.090 eV, and 1.377 eV respectively, which are in close agreement to the experimental results. The band gap values trend in this study is as： E9 （mBJ-GGA/LDA） 〉 E9 （GGA） 〉 Eg （LDA）. Optical parametric quantities （dielectric constant, refractive index, reflectivity and optical conductivity） which based on the band structure are aiso presented and discussed. BP, AlP, GaP, and InP have strong absorption in between the energy range 4-9 eV, 4-7 ev, 3-7 eV, and 2-7 eV respectively. Static dielectric constant, static refractive index and coefficient of reflectivity at zero frequency, within mBJ-GGA, are also calculated. BP, AIP, GaP, and InP show significant optical conductivity in the range 5.2-10 eV, 4.3-8 eV, 3.5- 7.2 eV, and 3.2-8 eV respectively. The present study endorses that the said compounds can be used in opto-electronic applications, for different energy ranges.展开更多
A detailed analysis of the electronic and structural properties of the filled tetrahedral semiconductors Li3AlP2 and Li3AlAs2 has been performed, using the full potential linearized augmented plane wave method within ...A detailed analysis of the electronic and structural properties of the filled tetrahedral semiconductors Li3AlP2 and Li3AlAs2 has been performed, using the full potential linearized augmented plane wave method within the density functional theory. Experimental results about the structural properties, involves the positions of the elements Al and P(As). Since there were not any other efforts about the positions of the Li elements in these compounds, so to our knowledge there was no theoretical study about them till now. In the first step the interactional forces between atoms were minimized. The calculated internal coordinations of atoms agree well with the experimental results. Using these positions we obtained the equilibrium lattice constants, bulk modulus and their pressure derivative. In the second step the electronic properties of Li3AlP2 and Li3AlAs2 have been studied. The study of total and partial electronic DOS indicate the main contribution of DOS consists of P(As) 3p(4p) and P(As) 3s(4s) states. Our band structure calculation verifies that Li3AlP2 is an indirect gap semiconductor with a value of about 2.36 eV between valance band maximum occuring at H point and conduction band minimum occuring at Г point;though the difference between the direct (2.38 eV) and indirect (2.36 eV) is very small. We also found that Li3AlAs2 is a direct band gap (1.49 eV) in the center of BZ.展开更多
The optical properties of CdBr2 were studied by first principle using the density functional theory. The dielectric functions and optical constants are calculated using the full potential-linearized augmented plane wa...The optical properties of CdBr2 were studied by first principle using the density functional theory. The dielectric functions and optical constants are calculated using the full potential-linearized augmented plane wave (FP-LAPW) method with the generalized gradient approximation (GGA). The theoretical calculated optical properties and energy Loss (EEL) spectrum yield a static refractive index of 2.1 and a plasmon energy of 13eV for hexagonal phase. The results, in comparison with the published data, are in good agreement with the experimental and previous theoretical results.展开更多
The optical properties of CdBr2 were studied by first principle using the density functional theory. The dielectric functions and optical constants are calculated using the full potential-linearized augmented plane wa...The optical properties of CdBr2 were studied by first principle using the density functional theory. The dielectric functions and optical constants are calculated using the full potential-linearized augmented plane wave (FP-LAPW) method with the generalized gradient approximation (GGA). The theoretical calculated optical properties and energy Loss (EEL) spectrum yield a static refractive index of 2.1 and a plasmon energy of 13eV for hexagonal phase. The results, in comparison with the published data, are in good agreement with the experimental and previous theoretical results.展开更多
The electronic structure, energy band structure, total density of states (DOS) and electronic density of perovskite SrTiO3 in the cubic phase are calculated by the using full potential-linearized augmented plane wave ...The electronic structure, energy band structure, total density of states (DOS) and electronic density of perovskite SrTiO3 in the cubic phase are calculated by the using full potential-linearized augmented plane wave (FP-LAPW) method in the framework density functional theory (DFT) with the generalized gradient approximation (GGA) by WIEN2k package. The calculated band structure shows a direct band gap of 2.5 eV at the Γ point in the Brillouin zone.The total DOS is compared with experimental x-ray photoemission spectra. From the DOS analysis, as well as charge-density studies, I have conclude that the bonding between Sr and TiO2 is mainly ionic and that the TiO2 entities bond covalently.The calculated band structure and density of state of SrTiO3 are in good agreement with theoretical and experimental results.展开更多
The optical properties of SrHfO3,were studied by first principle using the density functional theory.The dielectric functions and optical constants are calculated using the full potential–linearized augmented plane w...The optical properties of SrHfO3,were studied by first principle using the density functional theory.The dielectric functions and optical constants are calculated using the full potential–linearized augmented plane wave (FP-LAPW) method with the generalized gradient approximation(GGA)by Wien2k package. The theoretical calculated optical properties and energy loss(EEL)spectrum yield a static refractive index of1. 924and a Plasmon energy of 27eVfor cubic phase. The complex dielectric functions are calculated which are in good agreement with the available experimental results.展开更多
The electronic structure, band gap and density of states of (7,7) Armchair carbon nanotube by the full potentiallin- earized augmented plane wave (FP-LAPW)method in the framework density functional theory (DFT) with t...The electronic structure, band gap and density of states of (7,7) Armchair carbon nanotube by the full potentiallin- earized augmented plane wave (FP-LAPW)method in the framework density functional theory (DFT) with the generalized gradient approximation (GGA) were studied. The calculated band structure and density of state of Armchair (7,7) carbon nanotube were in good agreement with theoretical and experimental results.展开更多
基金Supported by UGC,New Delhi through UGC-BSR(JRF)fellowships
文摘Ab initio calculations are performed on the electronic, structural, elastic and optical properties of the cubic per- ovskite KCdF3. Tile Kohn Sham equations are solved by applying the full potential linearized augmented plane wave （FP-LAPW） method. The exchange correlation effects are included through the local density approximation （LDA ）, generalized gradient approximation （GGA） and modified Becke-Johnson （mBJ） exchange potential The calculated lattice constant is in good agreement with the experimental result. The elastic properties such as elastic constants, anisotropy factor, shear modulus, Young＇s modulus and Poisson＇s ratio are calculated. KCdF3 is ductile and elastically anisotropic. The calculations of the electronic band structure, density of states （DOS） and charge density show that this compound has an indirect energy band gap （M-F） with a mixed ionic and covalent bonding. The contribution of the different bands is analyzed from the total and partial density of states curves. Optical response of the dielectric functions, optical reflectivity, absorption coefficient, real part of optical conductivity, refractive index, extinction coefficient and electron energy loss, are presented for the energy range of O-40eV. The compound KCdF3 can be used for high-frequency optical and optoelectronic devices.
文摘Electronic structure and magnetic properties of wurtzite ZnO semiconductor doped with rare earth （RE=La, Ce, Pr, Pm, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm and Yb） atoms were studied using spin-polarized density functional theory based on the full-potential linear augmented plane wave （FP-LAPW） method as implemented in the Wien2k code. In this approach the generalized gradient approximation （GGA） was used for the exchange-correlation （XC） potential. Our results showed that the substitution of RE ions in ZnO induced spins polarized localized states in the band gap. Moreover, the studied DMSs compounds retained half metallicity at dopant concentration x=0.625%for most of the studied elements, with 100%spin polarization at the Fermi level （EF）. The total magnetic moments of these compounds existed due to RE 4f states present at EF, while small induced magnetic moments existed on other non-magnetic atoms as well. Finally, the energy difference between far and near configurations was investigated. It was found that the room temperature ferromagnetism was possible for RE-doped ZnO at near configuration. Since the RE-RE separation was long enough （far configuration） for magnetic coupling, the system became paramagnetic or antiferromagnetic ground state.
基金National Natural Science Foundation of China (50541036)
文摘The electronic structures of the titanium dioxide（TiO2） doped with V and Fe were analyzed by using first-principle calculations based on the density functional theory（DFT） with the full potential linearized augmented plane wave method （FP-LAPW）. The fully optimized structure and the relaxation introduced by impurity were obtained by minimizing the total energy and atomic forces. The unit cell of the V-doped anatase TiO2 is smaller than that of the non-doped one, but for the Fe-doped one, the case is just the opposite. It is found that the apical Ti-O and impurity-O bond lengths of the V/Fe-doped anatase TiO2 are greater than those of the non-doped structure, but smaller for the equatorial bond length. Through the band structures and the density of states, the V-doped TiO2 is shown to be a kind of half-metal, while the Fe-doped TiO2 a kind of metal. The magnetic moments of the V/Fe-doped system are mainly generated by the dopants. The results may be helpful for us to understand the experimental outcome of this system.
基金the Deanship of Scientific Research at King Saud University for funding this Prolific Research Group (PRG-1436-26)
文摘The mechanical, electronic and magnetic properties of non-magnetic MgTe and ferro-magnetic （FM） Mgo.75 TM025 Te （TM = Fe, Co, Ni） in the zinc-blende phase are studied by ab-initio calculations for the first time. We use the generalized gradient approximation functional for computing the structural stability, and mechanical properties, while the modified Becke and Johnson local （spin） density approximation （mBJLDA） is utilized for determining the electronic and magnetic properties. By comparing the energies of non-magnetic and FM calculations, we find that the compounds are stable in the FM phase, which is confirmed by their structural stabilities in terms of enthalpy of formation. Detailed descriptions of elastic properties of Mgo.75TMo.25Te alloys in the FM phase are also presented. For electronic properties, the spin- polarized electronic band structures and density of states are computed, showing that these compounds are direct bandgap materials with strong hybridizations of TM 3d states and Te p states. Further, the ferromagnetism is discussed in terms of the Zener free electron model, RKKY model and double exchange model. The charge density contours in the （110） plane are calculated to study bonding properties. The spin exchange splitting and crystal field splitting energies are also calculated. The distribution of electron spin density is employed in computing the magnetic moments appearing at the magnetic sites （Fe, Co, Ni）, as well as at the non-magnetic sites （Mg, Te）. It is found that the p-d hybridization causes not only magnetic moments on the magnetic sites but also induces negligibly small magnetic moments at the non-magnetic sites.
基金supported by the Project supported by the New Century Excellent Talents in University(Grant No.NCET-04-0702)National Natural Science Foundation of China(Grant No.50771047)
文摘Using the full potential linearized augmented plane wave FP-LAPW method within local density ap-proximation LDA, we have studied positron diffusion and surface emission in Cd-based semiconductors. This requires the calculation of electron and positron band structures. In the absence of experimental and theoretical data for CdX (X=S,Se,Te) we have treated the Si, which has been studied by several authors, as a test case. Predictive results on positron effective masses, deformation potentials, positron work functions, diffusion constants and positron mobilities are presented for CdX (X=S, Se, Te). Our calculated data for Si are compared with experimental and recent theoretical results.
基金Supported by (Foreign Academic Visitor Grant) of Universiti Teknologi Malaysia (UTM) Skudai,Johor,Malaysia for the Grant No.JI3000077264D035
文摘We report the electronic band structure and optical parameters of X-Phosphides （X=B, AI, Ga, In） by first-principles technique based on a new approximation known as modified Becke-Johnson （roB J）. This potential is considered more accurate in elaborating excited states properties of insulators and semiconductors as compared to LDA and GGA. The present calculated band gaps values of BP, AlP, GaP, and InP are 1.867 eV, 2.268 eV, 2.090 eV, and 1.377 eV respectively, which are in close agreement to the experimental results. The band gap values trend in this study is as： E9 （mBJ-GGA/LDA） 〉 E9 （GGA） 〉 Eg （LDA）. Optical parametric quantities （dielectric constant, refractive index, reflectivity and optical conductivity） which based on the band structure are aiso presented and discussed. BP, AlP, GaP, and InP have strong absorption in between the energy range 4-9 eV, 4-7 ev, 3-7 eV, and 2-7 eV respectively. Static dielectric constant, static refractive index and coefficient of reflectivity at zero frequency, within mBJ-GGA, are also calculated. BP, AIP, GaP, and InP show significant optical conductivity in the range 5.2-10 eV, 4.3-8 eV, 3.5- 7.2 eV, and 3.2-8 eV respectively. The present study endorses that the said compounds can be used in opto-electronic applications, for different energy ranges.
文摘A detailed analysis of the electronic and structural properties of the filled tetrahedral semiconductors Li3AlP2 and Li3AlAs2 has been performed, using the full potential linearized augmented plane wave method within the density functional theory. Experimental results about the structural properties, involves the positions of the elements Al and P(As). Since there were not any other efforts about the positions of the Li elements in these compounds, so to our knowledge there was no theoretical study about them till now. In the first step the interactional forces between atoms were minimized. The calculated internal coordinations of atoms agree well with the experimental results. Using these positions we obtained the equilibrium lattice constants, bulk modulus and their pressure derivative. In the second step the electronic properties of Li3AlP2 and Li3AlAs2 have been studied. The study of total and partial electronic DOS indicate the main contribution of DOS consists of P(As) 3p(4p) and P(As) 3s(4s) states. Our band structure calculation verifies that Li3AlP2 is an indirect gap semiconductor with a value of about 2.36 eV between valance band maximum occuring at H point and conduction band minimum occuring at Г point;though the difference between the direct (2.38 eV) and indirect (2.36 eV) is very small. We also found that Li3AlAs2 is a direct band gap (1.49 eV) in the center of BZ.
文摘The optical properties of CdBr2 were studied by first principle using the density functional theory. The dielectric functions and optical constants are calculated using the full potential-linearized augmented plane wave (FP-LAPW) method with the generalized gradient approximation (GGA). The theoretical calculated optical properties and energy Loss (EEL) spectrum yield a static refractive index of 2.1 and a plasmon energy of 13eV for hexagonal phase. The results, in comparison with the published data, are in good agreement with the experimental and previous theoretical results.
文摘The optical properties of CdBr2 were studied by first principle using the density functional theory. The dielectric functions and optical constants are calculated using the full potential-linearized augmented plane wave (FP-LAPW) method with the generalized gradient approximation (GGA). The theoretical calculated optical properties and energy Loss (EEL) spectrum yield a static refractive index of 2.1 and a plasmon energy of 13eV for hexagonal phase. The results, in comparison with the published data, are in good agreement with the experimental and previous theoretical results.
文摘The electronic structure, energy band structure, total density of states (DOS) and electronic density of perovskite SrTiO3 in the cubic phase are calculated by the using full potential-linearized augmented plane wave (FP-LAPW) method in the framework density functional theory (DFT) with the generalized gradient approximation (GGA) by WIEN2k package. The calculated band structure shows a direct band gap of 2.5 eV at the Γ point in the Brillouin zone.The total DOS is compared with experimental x-ray photoemission spectra. From the DOS analysis, as well as charge-density studies, I have conclude that the bonding between Sr and TiO2 is mainly ionic and that the TiO2 entities bond covalently.The calculated band structure and density of state of SrTiO3 are in good agreement with theoretical and experimental results.
文摘The optical properties of SrHfO3,were studied by first principle using the density functional theory.The dielectric functions and optical constants are calculated using the full potential–linearized augmented plane wave (FP-LAPW) method with the generalized gradient approximation(GGA)by Wien2k package. The theoretical calculated optical properties and energy loss(EEL)spectrum yield a static refractive index of1. 924and a Plasmon energy of 27eVfor cubic phase. The complex dielectric functions are calculated which are in good agreement with the available experimental results.
文摘The electronic structure, band gap and density of states of (7,7) Armchair carbon nanotube by the full potentiallin- earized augmented plane wave (FP-LAPW)method in the framework density functional theory (DFT) with the generalized gradient approximation (GGA) were studied. The calculated band structure and density of state of Armchair (7,7) carbon nanotube were in good agreement with theoretical and experimental results.
