Electronic structure and magnetic properties of the perovskite cerium manganese oxide from ab initio calculations

We have performed first-principle calculations of the structural, electronic and magnetic properties of cerium manganese oxide (CeMnO)₃, using full-potential linearized augmented plane-wave (FP-LAPW) scheme within GGA and GGA+U approaches. Features such as the lattice constant, bulk modulus and its pressure derivative are reported. Also, we have presented our results of the band structure and the density of states. The results show a half-metallic ferromagnetic ground state for CeMnO₃ in GGA+U treatment, whereas semi-metallic ferromagnetic character is observed in GGA. The results obtained, make the cubic CeMnO₃ a candidate material for future spintronic application.     

Ab initio study of electronic structure and magnetic properties in ferromagnetic Sr1−x(Mn,Cr)xO alloys

A first-principles approach is used to study the structural, electronic and magnetic properties of Sr_1−x(Mn, Cr)_xO alloys. The investigation was done using the (FP-LAPW) scheme within the generalized gradient approximation by Wu and Cohen (GGA-WC), GGA+U and LSDA+U. At ambient conditions our calculated results of band structures reveal that for Sr_1−x(Mn, Cr)_xO (for x=0.25 and 0.75) has a half-metallic (HM) band structure profile showing 100% spin polarization at the Fermi level. Therefore, the Sr_1−x(Mn, Cr)_xO (for x=0.25 and 0.75) is a candidate material for future spintronic/magnetoelectronics applications.     

Electronic band structure and optoelectronic properties of double perovskite Sr2MgMoO6 through modified Becke-Johnson potential

The crystal structure, electronic and optical properties of double perovskite Sr₂MgMoO₆ have been calculated by using the full-potential linear augmented plane wave (FP-LAPW) method. The band structure and density of states (DOS) were carried out by the modified Becke–Johnson (mBJ) exchange potential approximation based on the density functional theory (DFT). The calculated band structure shows a direct band gap (Γ–Γ) of 2.663 eV for Sr₂MgMoO₆. The compound Sr₂MgMoO₆ has a triclinic structure with the space group I-1, the lattice parameters a=5.5666 Å, b=5.5661 Å and c=7.9191 Å, which are used in our calculations. The optical parameters, like dielectric constant, refractive index, reflectivity and energy loss function were also calculated and analyzed. This work provides the first quantitative theoretical prediction of the optical properties and electronic structure for the triclinic phase of Sr₂MgMoO₆.     

Theoretical insight into the electronic and photocatalytic properties of Cu2O from a hybrid density functional theory

A comprehensive first-principle investigation, based on hybrid density functional theory, produces strong evidence that the Cu₂O band-edges do satisfy the requirements of the H⁺/H₂ and O₂/H₂O redox levels, demonstrating that it has enough driving force for photocatalytic overall water splitting. The calculated band gap of Cu₂O is 2.184 eV, which is consistent with the experimental value of 2.17 eV. The highly dispersive s–s hybrid states at the conduction band bottom result in a small effective mass of the electron, which is favorable to carrier separation and the carrier transfer to surface, and thus facilitate the reduction of H⁺ to H₂. The strong optical absorption of Cu₂O is beneficial to overall water splitting under visible light irradiation. Possible reasons for no observation of H₂ in some experiments are also discussed. The results address the ongoing controversy associated with photocatalytic overall water splitting of Cu₂O.     

Structural,elastic, electronic and thermodynamic properties of uranium filled skutterudites UFe4P12: First principle method

We present a theoretical study of structural, elastic, thermodynamic, and electronic properties of the uranium filled skutterudite UFe₄P₁₂. We use the full-potential linear muffin–tin orbital (FP-LMTO) method in which the local density approximation (LDA) is used for the exchange-correlation (XC) potential. The lattice parameter at equilibrium, the bulk modulus, its pressure derivative, the elastic constants and the band structure energy of the filled skutterudite UFe₄P₁₂ are calculated and systematically compared to available theoretical and experimental data. Herein, we use the total energy variation as function of strain technique to determine independent elastic constants and their pressure dependence. Furthermore, using quasi-harmonic Debye model with phonon effects, the effect of pressure P and temperature T on the lattice parameter, bulk modulus, thermal expansion coefficient, Debye temperature and the heat capacity of UFe₄P₁₂ are investigated for the first time. Band structure of UFe₄P₁₂ indicates a tendency of forming a pseudo-gap that appears above the Fermi level at Γ point. This is a unique characteristic of skutterudite, especially when a single phosphorous p-band crosses the Fermi level. The crossing band is, indeed, pushed down by the repulsion of U f-resonance states.     

Electronic structure,chemical bonding and optical properties of Di-2-pyrymidonium dichloride diiodide (C4H5ClIN2O) from first-principles

The electronic structure and electronic charge density of the monoclinic phase Di-2-pyrymidonium dichloride-di-iodide compound is studied by using the local density approximation (LDA) and Engel Vosko generalized gradient approximation (EVGGA). Using LDA for exchange correlation potential, we have optimized the atomic positions taken from the X-ray crystallographic data by minimization of the forces acting on the atoms. From the relaxed geometry the electronic structure, electronic charge density and the optical properties were determined. Band structures disclose that this compound has indirect energy band gap. The obtained energy band gap value using EVGGA (2.010 eV) is larger than that obtained within LDA (1.781 eV). To envision the chemical bonding nature between the composition of the investigated compound, the distribution of charge density was discussed in the (−1 0 1) crystallographic plane. The contour plot shows partial ionic and strong covalent bonding between C–O, N–C and C–H atoms. The optical properties of Di-2-pyrymidonium dichloride-di-iodide are obtained by the calculation of the dielectric function.     

Electronic structure,effective mass,and optical dispersion of 2-mercapto-5-methyl-1,3,4-thiadiazole: density functional theory calculations

Density functional theory was used to calculate the electronic band structure, effective mass, and optical dispersion of 2-mercapto-5-methyl-1,3,4-thiadiazole (MMTD). The all-electron, full-potential, linearized augmented plane wave method was used. The exchange correlation potential was treated using the local density approximation, generalized gradient approximation, and modified Becke Johnson approximation. The calculated band structure shows that MMTD has a direct energy bandgap. The partial density of states revealed strong hybridization between N p, C p, N s, and H s orbitals. The electronic charge density distribution confirmed partial ionic and strong covalent C–N, C–C, C–H, and N–N bonds. We also calculated the optical dielectric function and related optical properties (refractive index, extinction coefficient, absorption coefficient, and reflectivity).     

Electronic structure and magnetic properties of Ca3Co2O6 cobaltites: Intrachain magnetic ordering

The present study is focussed on the intrachain magnetic interactions between the trigonal prismatic (TP) and octahedral (OCT) Co sites in Ca₃Co₂O₆ cobaltites from their electronic structure determined using the first principle full potential linearized augmented plane wave method within the GGA+U approximation. The occurence of various magnetic solutions as a function of the Coulomb integral U of the GGA+U approach is investigated. Various magnetic configurations, corresponding to different total magnetization, are found only when the insulating state is reached for U > 2.5 eV and the most stable solution corresponds to a magnetic spin moment on the TP (respectively OCT) site around 2.6 (respectively 1) Bohr magneton.     

New insights into a first principle calculation and experimental study of Sn-Pb-Ge ternary-metal perovskites for potential photovoltaic application

To replace Pb with a less toxic metal is a key scientific challenge because of the toxicity of Pb and the most viable replacement are Sn and Ge. In this study, we propose Sn-Pb-Ge ternary-metal perovskites CH₃NH₃Sn_xPb_yGe_1-x-yI₃ (0 < x, y < 1) for the first time. For the identification of new families, the features were verified by fist principle calculations from a theoretical perspective, especially the structural and electric performance, optical property and crystal structure. The Sn-Pb-Ge ternary-metal perovskites are prepared for from the aqueous HI/H₃PO₂ solvent mixture the first time, For CH₃NH₃Sn_0.25Pb_0.5Ge_0.25I₃, the computed results are in good agreement with the experimental data, which provide a clear-sighted insight into the design of environmentally friendly perovskites for potential electrical and tunable optical application.     

First principles study of structural,electronic and optical properties of indium gallium nitride arsenide lattice matched to gallium arsenide

First principles calculations in the framework of the full-potential linearized augmented plane wave (FP-LAPW) scheme have been carried out. The dilute-nitride zinc blende (In_xGa_1−xN_yAs_1−y) was modeled at selected nitrogen compositions of y=3.125%, 6.25% and 9.375% lattice matched to gallium arsenide (GaAs). We pay attention to the In_xGa_1−xN_yAs_1−y alloy which can be perfectly lattice matched to the GaAs over its entire compositional range. In our study, this is achieved when a condition y~2.7x is maintained. The band structure calculations were performed with and without relaxation by using the generalized gradient approximation of Engel and Vosko (EV-GGA) as well as by the modified Becke–Johnson potential exchange (TB-mBJ). The action of the localized potential of subsisted nitrogen atoms was attributed to effect of relaxation. Increasing both indium and nitrogen compositions leads to decreasing energy band gap. In addition a band anti-crossing model (BAC) was also adopted to study the composition dependence of the direct band gap of quaternary alloys, building a bridge between their electronic and linear optical properties.     

碳纳米管的电子能带结构和态密度研究

为了研究单壁碳纳米管的电子能带特性及其态密度,本文采用紧束缚法和态密度函数,对无限长碳纳米管进行了理论计算和模拟。结果表明:碳纳米管的电子能带结构与其几何结构密切相关,一般认为扶手型管呈现出金属性;而锯齿管则不同,当n=3k(k为整数)时,其能级存在一个较小的禁带宽度,具有半金属性质;而其它锯齿型管均存在较大的禁带宽度,且禁带宽度随管径的增大而减小,具有半导体性质,这为碳纳米管的电子结构的研究提供了必要且有价值的理论依据。     

Structural,electronic, mechanical and magnetic properties of rare-earth nitrides REN (RE=Ce,Pr, Nd): A first principles study

The structural stability of rare earth nitrides REN (RE=Ce,Pr,Nd) is investigated among three cubic structures, namely, NaCl (B1), CsCl(B2) and zinc blende (B3). It is found that NaCl structure is the most stable structure for all the three nitrides. On increasing the pressure, structural phase transition from NaCl (B1) to CsCl (B2) phase is predicted in CeN and NdN at the pressures of 88 GPa and 36.5 GPa while NaCl (B1) to zinc blende (B3) phase transition is observed in PrN at the pressure of 68 GPa. At normal pressure, all the three nitrides are stable in the ferromagnetic state (FM) with cubic NaCl (B1) structure. The calculated lattice parameters and bulk modulus values are in good agreement with experimental and other theoretical values. Electronic structure reveals that PrN and NdN are half metallic while CeN is metallic at normal pressure. Ferromagnetism is quenched in CeN and PrN at the pressures of 152 GPa and 121 GPa respectively. The positive values of elastic constants indicate that all the three nitrides are mechanically stable in NaCl Phase. It is found that all these nitrides are ductile and anisotropic in nature.     

First principles study of electronic and optical properties of the ternary SnSb4S7 using modified Becke-Johnson potential

The electronic and optical properties of SnSb₄S₇ compound are calculated by the full-potential linearized augmented plane-wave (FP-LAPW) method. The density of states (DOS) is carried out by the modified Becke-Johnson (mBJ) exchange potential approximation based on density functional theory (DFT). The compound SnSb₄S₇ has a monoclinic structure with the space group P2₁/m with lattice parameters of a=11.331 Å, b=3.865 Å and c=13.940 Å. The band gap is calculated to be 0.8 eV. The optical parameters, like dielectric constant, refractive index, reflectivity and energy loss function were also calculated and analyzed. The present work provides information about variation of the electronic and optical properties which reveals that SnSb₄S₇ is suitable for optoelectronic devices.     

First-principles calculations of electronic structure and optical properties of boron–phosphorus co-doped zinc oxide

This paper presents the electronic structure and optical properties of boron–phosphorus co-doped zinc oxide ((B, P) codoped ZnO) systems employing first principles calculations based on density functional theory. In the (B, P) codoped ZnO systems, dopants prefer to be located on the nearest-neighbor sites in the same (00l) plane forming B_Zn–P_O complex with binding energy of −1.92 eV; some hole sates appear above the valence band maximum. With increase in P concentration, P 3p states become more and more delocalized. The calculated optical properties indicate that strong optical transitions in lower energy region occur; the intensities and positions of these peaks are P concentration-dependent, which could be ascribed to the electronic transitions between P 3p and Zn 4s states. Moreover, the absorption coefficients and other optical constants of the (B, P) codoped ZnO systems, such as reflectivity, refractive index, and loss function, are also discussed.     

First principles study of structural,electronic, elastic and magnetic properties of gadolinium hydride system GdHx (x=1, 2, 3)

The structural, electronic, elastic and magnetic properties of gadolinium and its hydrides GdH_x (x=1, 2, 3) are investigated by using Vienna ab-initio simulation package with the generalized gradient approximation parameterized by Perdew, Burke and Ernzerhof (GGA-PBE) plus a Hubbard parameter (GGA-PBE+U) in order to include the strong Coulomb correlation between localized Gd 4f electrons. At ambient pressure all the hydrides are stable in the ferromagnetic state. The calculated lattice parameters are in good agreement with the experimental results. The bulk modulus is found to decrease with the increase in the hydrogen content for the gadolinium hydrides. A pressure-induced structural phase transition is predicted to occur from cubic to hexagonal phase in GdH and GdH₂ and from hexagonal to cubic phase in GdH₃. The electronic structure reveals that mono and di-hydrides are metallic, whereas trihydride is half-metallic at normal pressure. On further increasing the pressure, a half-metallic to metallic transition is also observed in GdH₃. The calculated magnetic moment values of GdH_x (x=1, 2, 3) are in accord with the experimental values.     

HfxTi1-xO2电子结构与光学性质的第一性原理研究

利用基于密度泛函理论的平面波超软赝势法,研究了金红石结构TiO2以及不同比例Hf替代Ti原子后形成的化合物HfxTi1-xO2的几何结构、电子结构和光学性质.计算结果表明,化合物HfxTi1-xO2都是具有间接带隙的半导体,Hf的替代使TiO2的禁带宽度有不同程度的增加,静态光学介电常数减小,但均高于SiO2,因此能够满足微电子行业对于高k材料的要求.     

Electronic Structure and Thermoelectric Properties of Si-Based Clathrate Compounds

Thermoelectric properties of Au-substituted Si-based clathrates, Ba₈AuGa₁₃Si₃₂ and Ba₆A₂AuGa _x Si_45−x (A = Sr, Eu, x = 13, 14), were experimentally and theoretically investigated. The polycrystalline samples of the Au-substituted Si-based clathrates were prepared by using the spark plasma sintering technique. The electronic structure of Ba₆A₂AuGa₁₃Si₃₂ was theoretically calculated by ab initio calculations, and the thermoelectric properties of Ba₆A₂AuGa _x Si_45−x were estimated through the calculated electronic structure. The effective mass of Ba₆A₂AuGa _x Si_45−x was experimentally estimated to be greater than that of Ba₈AuGa₁₃Si₃₂. Experimentally observed electronic properties agree with the calculations for Ba₆A₂AuGa _x Si_45−x . The maximum ZT value of Ba₆Sr₂AuGa₁₄Ge₃₁ is about 0.5 at 850 K. The calculated thermoelectric properties agree very well with the experimental results in the range from room temperature to 900 K.     

Electronic structure of stable n-type semiconducting molecular complex (diC8-BTBT)(TCNQ) studied by ultraviolet photoemission and inverse photoemission spectroscopy

The electronic structure of a semiconducting mixed-stack charge transfer (CT) complex composed of a 2,7-dialkyl[1]benzothieno[3,2-b][1] benzothiophene (diC₈-BTBT) electron donor and a tetracyanoquinodimethane (TCNQ) electron acceptor, (diC₈-BTBT)(TCNQ), was studied by ultraviolet photoemission spectroscopy and inverse photoemission spectroscopy. Compared with its components, the frontier electronic states observed for the (diC₈-BTBT)(TCNQ) complex showed a large stabilization that originates from the reconstruction of electronic states by intermolecular donor-acceptor CT interactions. We discuss how the frontier electronic states of the complex are formed from those of the individual component molecules, and clarify the origin of the air-stable n-type organic field-effect transistor characteristics that the material exhibits when it is used as a channel semiconductor.