First-principles study of the optical properties of defect electronic structure and chalcopyrite CdGa2Te4

The electronic and optical properties of the defect chalcopyrite CdGa2Te4 compound are studied based on the first- principles calculations. The band structure and density of states are calculated to discuss the electronic properties and orbital hybridized properties of the compound. The optical properties, including complex dielectric function, absorption coefficient, refractive index, reflectivity, and loss function, and the origin of spectral peaks are analysed based on the electronic structures. The presented results exhibit isotropic behaviours in a low and a high energy range and an anisotropic behaviour in an intermediate energy range.

Electronic structure and optical properties of Mg_xZn_(1-x)S bulk crystal using first-principles calculations

We perform the first-principles calculations within the framework of density functional theory to determine the elec- tronic structure and optical properties of MgxZnl-xS bulk crystal. The results indicate that the electronic structure and optical properties of MgxZnl_xS bulk crystal are sensitive to the Mg impurity composition. In particular, the MgxZnl-xS bulk crystal displays a direct band structure and the band gap increases from 2.05 eV to 2.91 eV with Mg dopant compo- sition value x increasing from 0 to 0.024. The S 3p electrons dominate the top of valence band, while the Zn 4s electrons and Zn 3p electrons occupy the bottom of conduction band in MgxZnl_xS bulk crystal. Moreover, the dielectric constant decreases and the optical absorption peak obviously has a blue shift. The calculated results provide important theoretical guidance for the applications of MgxZn1-xS bulk crystal in optical detectors.

Electronic structures and optical properties of HfO_2–TiO_2 alloys studied by first-principles GGA + U approach

The phase diagram of HfO_2–TiO_2 system shows that when Ti content is less than 33.0 mol%, HfO_2–TiO_2 system is monoclinic; when Ti content increases from 33.0 mol% to 52.0 mol%, it is orthorhombic; when Ti content reaches more than 52.0 mol%, it presents rutile phase. So, we choose the three phases of HfO_2–TiO_2 alloys with different Ti content values. The electronic structures and optical properties of monoclinic, orthorhombic and rutile phases of HfO_2–TiO_2 alloys are obtained by the first-principles generalized gradient approximation（GGA） ＋U approach, and the effects of Ti content and crystal structure on the electronic structures and optical properties of HfO_2–TiO_2 alloys are investigated. By introducing the Coulomb interactions of 5 d orbitals on Hf atom（U_1~d）, those of 3 d orbitals on Ti atom（U_2~d）, and those of 2 p orbitals on O atom（Up） simultaneously, we can improve the calculation values of the band gaps, where U_1~d, U_2~d, and Up values are 8.0 eV, 7.0 eV, and 6.0 eV for both the monoclinic phase and orthorhombic phase, and 8.0 eV, 7.0 eV, and 3.5 eV for the rutile phase. The electronic structures and optical properties of the HfO_2–TiO_2 alloys calculated by GGA ＋U_1~d（U_1~d= 8.0 eV） ＋U_2~d（U_2~d= 7.0 eV） ＋U^p（U^p= 6.0 eV or 3.5 eV） are compared with available experimental results.

First-Principles Study of Electronic Structure and Optical Properties of Silicon/Carbon Nanotube

A supercell of a nanotube formed by a carbon nanotube (CNT) and a silicon nanotube (SiNT) is established. The electronic structure and optical properties are implemented through the first-principles method based on the density functional theory (DFT) with the generalized gradient approximation (GGA). The calculated results show that (6, 6) - (6, 6) silicon/carbon nanotubes (Si/CNTs) presented a direct band gap of 0.093 eV, (4, 4) - (6, 6) silicon/carbon nanotubes presented a direct band gap of 0.563 eV. The top of valence band was fundamentally determined by the Si-3p states and C-2p states, and the bottom of conduction band was primarily occupied by the C-2p states and Si-3p states in the Si/CNTs. It was found that (6, 6) - (6, 6) Si/CNTs have smaller energy band gap and better conductivity. Besides, Si/CNTs have satisfactory absorption characteristics and luminous efficiency in ultraviolet band.

Electronic and optical properties of GaN–MoS2 heterostructure from first-principles calculations

Heterostructures(HSs)have attracted significant attention because of their interlayer van der Waals interactions.The electronic structures and optical properties of stacked GaN-MoS2 HSs under strain have been explored in this work using density functional theory.The results indicate that the direct band gap(1.95 e V)of the Ga N-MoS2 HS is lower than the individual band gaps of both the GaN layer(3.48 e V)and the MoS2 layer(2.03 eV)based on HSE06 hybrid functional calculations.Specifically,the GaN-MoS2 HS is a typical type-II band HS semiconductor that provides an effective approach to enhance the charge separation efficiency for improved photocatalytic degradation activity and water splitting efficiency.Under tensile or compressive strain,the direct band gap of the GaN-MoS2 HS undergoes redshifts.Additionally,the GaN-MoS2 HS maintains its direct band gap semiconductor behavior even when the tensile or compressive strain reaches 5%or-5%.Therefore,the results reported above can be used to expand the application of Ga N-MoS2 HSs to photovoltaic cells and photocatalysts.

Effects of N-doping concentration on the electronic structure and optical properties of N-doped β-Ga_2O_3

The electronic structures and the optical properties of N-doped β-Ga2O3 with different N-doping concentrations are studied using the first-principles method.We find that the N substituting O（1） atom is the most stable structure for the smallest formation energy.After N-doping,the charge density distribution significantly changes,and the acceptor impurity level is introduced above the valence band and intersects with the Fermi level.The impurity absorption edges appear to shift toward longer wavelengths with an increase in N-doping concentration.The complex refractive index shows metallic characteristics in the N-doped β-Ga2O3.

Electronic structures and thermoelectric properties of solid solutions CuGa_(1-x) In_xTe_2 : A first-principles study

The electronic structures of solid solutions CuGal_xlnxTe2 are systematically investigated using the full-potential all-electron linearized augmented plane wave method. The calculated lattice parameters almost linearly increase with the increase of the In composition, which are in good agreement with the available experimental results. The calculated band structures with the modified Becke-Johnson potential show that all solid solutions are direct gap conductors. The band gap decreases linearly with In composition increasing. Based on the electronic structure calculated, we investigate the thermoelectric properties by the semi-classical Boltzmann transport theory. The results suggest that when Ga is replaced by In, the bipolar effect of Seebeck coefficient S becomes very obvious. The Seebeck coefficient even changes its sign from positive to negative for p-type doping at low carrier concentrations. The optimal p-type doping concentrations have been estimated based on the predicted maximum values of the power factor divided by the scattering time.

Electronic structure and optical properties of Al and Mg co-doped GaN

The electronic structure and optical properties of A1 and Mg co-doped GaN are calculated from first principles using density function theory with the plane-wave ultrasoft pseudopotentiai method. The results show that the optimal form of p-type GaN is obtained with an appropriate AI：Mg co-doping ratio rather than with only Mg doping. A1 doping weakens the interaction between Ga and N, resulting in the Ga 4s states moving to a high energy region and the system band gap widening. The optical properties of the co-doped system are calculated and compared with those of undoped GaN. The dielectric function of the co-doped system is anisotropic in the low energy region. The static refractive index and reflectivity increase, and absorption coefficient decreases. This provides the theoretical foundation for the design and application of A1-Mg co-doped GaN photoelectric materials.

First-principles calculations on the electronic structure and optical properties of BaSi_2

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.

Effect of warpage on the electronic structure and optical properties of bilayer germanene

The electronic structure and optical properties of bilayer germanene under different warpages are studied by the first-principles method of density functional theory.The effects of warpages on the electronic structure and optical properties of bilayer germanene are analyzed.The results of the electronic structure study show that the bottom of the conduction band of bilayer germanene moves to the lower energy direction with the increase of warpages at the K point,and the top of the valence band stays constant at the K point,and so the band gap decreases with the increase of warpage.When the warpage is 0.075 nm,the top of the valence band of bilayer germanene changes from K point to G point,and the bilayer germanene be-comes an indirect band gap semiconductor.This is an effective means to modulate the conversion of bilayer germanene between direct band gap semiconductor and indirect band gap semiconductor by adjusting the band structure of bilayer ger-manene effectively.The study of optical properties shows that the effect of warpage on the optical properties of bilayer ger-manene is mainly distributed in the ultraviolet and visible regions,and the warpage can effectively regulate the electronic struc-ture and optical properties of bilayer germanene.When the warpage is 0.069 nm,the first peak of dielectric function and extinc-tion coefficient is the largest,and the energy corresponding to the absorption band edge is the smallest.Therefore,the elec-tron utilization rate is the best when the warpage is 0.069 nm.

Electronic Structure and Optical Properties of K2Ti6O13 Doped with Transition Metal Fe or Ag

Based on the experimental study of the optical properties of K2Ti6O13 doped with Fe or Ag,their electronic structures and optical properties are studied by the rst-principles method based on the density functional theory(DFT).The calculated optical properties are consis-tent with the experiment results.K2Ti6O13 doped with substitutional Fe or Ag has isolated impurity bands mainly stemming from the hybridization by the Fe 3d states or Ag 4d states with Ti 3d states and O 2p states and the band gap becomes narrower,the absorption edge of K2Ti6O13 thus has a clear red shift and the absorption of visible light can be realized after doping.For Fe-doped K2Ti6O13,the impurity bands are in the middle of the band gap,suggesting that they can be used as a bridge for valence band electrons transition to the conduction band.For Ag-doped K2Ti6O13,the impurity bands form a shallow accep-tor above the valence band and can reduce the recombination rate of photoexcited carriers.The experimental and calculated results are signi cant for the development of K2Ti6O13 materials that have absorption under visible light.

The First Principle Calculation of Electronic Structure and Optical Properties of CdGeAs_2

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.

Electronic structure and optical properties of rutile RuO_2 from first principles

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.

First-principles study of the structural,elastic,and optical properties for Sr_(0.5)Ca_(0.5)TiO_3

A detailed theoretical study of the structural, elastic, and optical properties for Sr0.5Ca0.5TiO3 is carried out by first- principles calculations. The band structure exhibits a direct bandgap of 2.08 eV at the F point in the Brillouin zone. The bulk modulus, shear modulus, Young＇s modulus, and Poisson＇s ratio are derived based on the calculated elastic constants. The bulk modulus B = 153 GPa and shear modulus G = 81GPa are in good agreement with available experimental data. Poisson＇s ratio v = 0.275 suggests that Sr0.sCa0.sTiO3 should be classified as being a ductile material. Using the electronic band structure and density of states, we analyze the interband contribution to the optical properties. The real and imaginary parts of the dielectric function, as well as the optical properties such as the optical absorption coefficient, refractive index, extinction coefficient, and energy-loss spectrum are calculated. The static dielectric constant ε1 （0） and the refractive index n（0） are also investigated.

Electronic structures and optical properties of Si-and Sn-doped β-Ga_2O_3: A GGA+U study

The electronic structures and optical properties of β-Ga_2O_3 and Si-and Sn-doped β-Ga_2O_3 are studied using the GGA + U method based on density functional theory. The calculated bandgap and Ga 3d-state peak of β-Ga_2O_3 are in good agreement with experimental results. Si-and Sn-doped β-Ga_2O_3 tend to form under O-poor conditions, and the formation energy of Si-doped β-Ga_2O_3 is larger than that of Sn-doped β-Ga_2O_3 because of the large bond length variation between Ga–O and Si–O. Si-and Sn-doped β-Ga_2O_3 have wider optical gaps than β-Ga_2O_3, due to the Burstein–Moss effect and the bandgap renormalization effect. Si-doped β-Ga_2O_3 shows better electron conductivity and a higher optical absorption edge than Sn-doped β-Ga_2O_3, so Si is more suitable as a dopant of n-type β-Ga_2O_3, which can be applied in deep-UV photoelectric devices.

First-Principles Investigation of Energetics and Electronic Structures of Ni and Sc Co-Doped MgH2

First-principles calculations were used to study the energetics and electronic structures of Ni and Sc co-doped MgH2 system. The preferential positions for dopants were determined by the minimal total electronic energy. The results of formation enthalpy indicate that Ni and Sc co-doped MgH2 system is more stable than Ni single-doped system. The hydrogen desorption enthalpies of these two hydrides are investigated. Ni and Sc co-doping can improve the dehydrogenation properties of MgH2. The lowest hydrogen desorption enthalpy of 0.30 eV appears in co-doped system, which is significantly lower than that of Ni doping. The electronic structure analysis illustrates that the hybridization of dopants with Mg and H atom together weakens the Mg-H interaction. And the Mg-H bonds are more susceptible to dissociate by Ni and Sc co-doping because of the reduced magnitude of Mg-H hybridization peaks. These behaviors effectively improve the dehydrogenation properties of Ni and Sc co-doped cases.

First-principles study of the electronic structures and optical properties of C-F-Be doped wurtzite ZnO

The electronic structure and optical properties of pure, C-doped, C~ codoped and C-F-Be cluster- doped ZnO with a wurtzite structure were calculated by using the density functional theory with the plane-wave ultrasoft pseudopotentials method. The results indicate that p-type ZnO can be obtained by C incorporation, and the energy level of Co above the valence band maximum is 0.36 eV. The ionization energy of the complex Zn16O14CF and ZnlsBeO14CF can be reduced to 0.23 and 0.21 eV, individually. These results suggest that the defect complex of ZnlsBeO14CF is a better candidate for p-type ZnO. To make the optical properties clear, we investigated the imaginary part of the complex dielectric function ofundoped and C-F-Be doped ZnO. We found that there is strong absorption in the energy region lower than 2.7 eV for the C-F-Be doped system compared to pure ZnO.

Effect of N and Fe codoping on the electronic structure and optical properties of TiO_2 from first-principles study

The electronic structure and optical properties of N and Fe codoping Ti02 have been investigated by first-principles calculations based on density functional theory. The calculated results indicate that the stability of N and Fe codoping TiO2 will change at different substitutional sites of N and Fe. The mechanism of band gap narrowing of doping Ti02 is discussed by investigating the density of state. The different substitutional site of N and Fe in codoping TiO2 influences the visible-light absorption. An increased visible-light absorption for doping TiO2 results from the synergistic effect of N and Fe codoping. Therefore, N and Fe codoping may enhance the visible-light photocatalytic activity of TiO2.

Electronic structure and optical properties of the scintillation material wurtzite ZnS(Ag)

In order to investigate the effect of Ag doping(ZnS(Ag)) and Zn vacancy(V_(Zn)) on the alpha particle detection performance of wurtzite(WZ) ZnS as a scintillation cell component, the electronic structure and optical properties of ZnS, ZnS(Ag), and V_(Zn)were studied by firstprinciple calculation based on the density functional theory. The results show that the band gaps of ZnS, ZnS(Ag),and V_(Zn)are 2.17, 1.79, and 2.37 eV, respectively. Both ZnS(Ag) and V_(Zn)enhance the absorption and reflection of the low energy photons. A specific energy, about 2.9 eV,leading to decrease of detection efficiency is observed. The results indicate that Ag doping has a complex effect on the detection performance. It is beneficial to produce more visible light photons than pure WZ ZnS when exposed to the same amount of radiation, while the increase of the absorption to visible light photons weakens the detection performance. Zn vacancy has negative effect on the detection performance. If we want to improve the detection performance of WZ ZnS, Ag doping will be a good way,but we should reduce the absorption to visible light photons and control the number of Zn vacancy rigorously.

Electronic structure and optical properties of plutonium dioxide from first-principles calculations

The electronic structure and optical properties of plutonium dioxide were calculated using the generalized gradient approximation with a Hubbard parameter U （GGA ＋ U） for considering the strong coulomb correlation between localized Pu of electrons based on the first-principles density functional theory. The calculated results show that PuO2 is a semiconductor material with the band gap of 1.8 eV, which is in good agreement with the corresponding experimental data. Furthermore, the dielectric function, reflectivity, refractive index, and extinction coefficient were calculated and analyzed using the Kramers-Kronig relationship for PuO2. The calculated results were compared with the experimental data from the published literature.