Full-potential Linear Muffin-tin Orbital Research Articles

Electronic properties of cubic ScGaAs and ScGaN ternaries and superlattices

The electronic properties of both Sc x Ga 1− x As and Sc x Ga 1− x N ternary alloy and superlattice systems are investigated within the first-principles full-potential linear muffin-tin orbitals method (FPLMTO) in its atomic sphere approximation (ASA) using the technique of empty spheres, which allows an accurate treatment of the interstitial regions. The phase transition from the rocksalt (B1) to the zinc blende (B3) structure is investigated and the possibility of zinc blende/zinc blende GaN/Sc x Ga 1− x N and GaAs/Sc x Ga 1− x As superlattices is expected. Wide and direct gaps are found to be possible in these systems, predicting them as good candidates for optoelectronic applications.

Structural phase transition, elastic properties and electronic properties of chalcopyrite CuAlX2 (X=S, Se, Te)

Abstract The density functional theory calculations of structural phase transition, elastic constants and electronic structure of the CuAlX 2 (X = S, Se, Te) have been reported using the full potential linear muffin-tin orbital (FP-LMTO). In this approach, the local density approximation is used for the exchange-correlation potential. Results are given for lattice constant, bulk modulus, and its pressure derivative, band structure, density of states and pressure dependence of energy gaps. We note that these compounds are semiconductors with direct energy gaps. The valence-band maximum and conduction-band minimum are located at Γ . Our results are compared with previous theoretical calculations and experimental data. The elastic constants at equilibrium in BCT structure are also determined.

Structural phase transition and elastic properties of Curium and Uranium monobismuthides under pressure effect

A density functional (DFT) calculations of the structural, elastic and high pressure properties of the cubic XBi (X=U,Cm) compounds, has been reported using the full potential linear muffin-tin orbital (FP-LMTO) method. In this approach the local density approximation (LDA) is used for the exchange-correlation (XC) potential. Results are given for lattice constant, bulk modulus and its pressure derivatives. The pressure transitions at which these compounds undergo structural phase transition from NaCl-type (B1) to CsCl-type (B2) phase were found to be in good agreement with the available theoretical results. We have determined the elastic constants C 11, C 12, C 44 and their pressure dependence which have not been established experimentally or theoretically.

Structural and elastic properties of antiperovskites XNBa3 (X=As, Sb) under pressure effect

Abstract First-principle calculations of structural, elastic and high pressure properties of antiperovskites XNBa 3 ( X =As, Sb) are performed, using the full-potential linear muffin-tin orbital (FP-LMTO) method. The local density approximation (LDA) is used for the exchange-correlation (XC) potential. Results are given for lattice constant, bulk modulus and its pressure derivatives. We have determined the elastic constants C 11 , C 12 and C 44 and their pressure dependence. We derived shear moduli, Young's modulus, Poisson's ratio and Lame's constants for ideal polycrystalline XNBa 3 aggregates. By analyzing the ratio of the bulk to shear moduli, we conclude that XNBa 3 compounds are brittle in nature. We estimated the Debye temperature of XNBa 3 from the average sound velocity. This is the first quantitative theoretical prediction of the elastic properties of AsNBa 3 and SbNBa 3 compounds, and it still awaits experimental confirmation.

First-principles study of phase transition and structural properties of AlAs

We have investigated the phase transition and structural properties of AlAs in three crystallographic structures, i.e., B3 (zinc blende), B1 (rocksalt), and B8 (nickel arsenide), at high pressures using the full-potential linearized muffin-tin orbital (FP-LMTO) scheme within the generalized gradient approximation correction (GGA) in the frame of density functional theory (DFT). For B8 structure, it is found that the c/ a ratios kept nearly constant (∼0.2% fluctuation) corresponding to V/ V 0 ∼ 0.7–1.05 ( V is the primitive cell volume and V 0 is the experimental equilibrium volume of B3 structure), which is in full agreement with experiment, but the c/ a ratios increase linearly with the values of V/ V 0 decreasing corresponding to V/ V 0 ∼ 0.4–0.7. This indicates under low pressure the compression along c-axis and a-axis is the same, but the compression along c-axis is more difficult than along a-axis under higher pressure. Based on the condition of equal enthalpies AlAs is found to undergo a structural phase transition from B3 to B8 at 5.34 GPa, in agreement with the experimental value of 7 ± 5 GPa, and is speculated to undergo the B3– B1 transition at 6.24 GPa.

Electronic structure of ScN, YN, LaN and GdN superlattices

Using the plane wave version of the full potential linear muffin-tin orbital (FPLMTO) method, which enables an accurate treatment of the interstitial regions, the electronic properties of ScN, YN, LaN and GdN rocksalt/rocksalt superlattices are calculated. It is found that apart from YN/ScN, all the other superlattices have negative bandgaps. However, it is shown that these systems can be semiconductors if a correction is made to the local density approximation (LDA).

FP-LMTO investigations of mechanical stability and high pressure of platinum nitride compounds

We report local density functional calculations using the full potential linear muffin-tin orbital (FP-LMTO) method for binary platinum nitride (PtN), in five different crystal structures, the rock salt (B1), zinc-blende (B3), wurtzite (B4), nickel arsenide (B8), and PbS (B10) phases. The ground state properties such as the equilibrium lattice constant, elastic constants, the bulk modulus and its pressure derivative of PtN in these phases are determined and compared with the other available experimental and theoretical works. Our calculations confirm in the B3 structure that PtN is found to be mechanically stable with a large bulk modulus B=232.45 GPa and at a sufficiently high pressure the B8 1 structure would be favoured. The theoretical transition pressure from zinc blende (B3) to NiAs (B8 1), zinc-blende (B3) to rock-salt (B1) and zinc-blende (B3) to PbO (B10) is determined to be 9.10 GPa, 9.85 GPa and 69.35 GPa, respectively. Our calculation shows also in five different structures for PtN a high bulk modulus is a good indicator of a hard material.

FP-LMTO calculations of elastic and electronic properties of the filled skutterudite CeRu 4P 12

First-principles calculations have been used to investigate the structural, electronic and elastic properties of the filled skutterudite CeRu 4P 12, using the full-potential linear muffin-tin orbital (FP-LMTO) method. The exchange-correlation energy is described in the local spin density approximation (LSDA) using the Perdew–Wang parameterization. The results of the electronic properties show that this compound is an indirect band gap material. A special interest has been made to the determination of the elastic constants since there have been no available experimental and theoretical data. The energy band gaps and their volume and pressure dependence are investigated. Our results of the ground-state electronic properties are found to agree with experimental results.

Theoretical investigation of the electronic and optical properties of Zn 2OX (X = S, Se, Te) in chalcopyrite phase by full potential methods

A full potential linear muffin tin orbital (FP-LMTO) and linear augmented plane wave plus local orbital (APW + lo) approach is used to investigate the electronic and optical properties of Zn 2OX (X = S, Se, Te) in the chalcopyrite phase. It is found that these compounds are direct band semiconductors and the value of band gap increases as one move from Te to S. The optical properties of these compounds namely the reflectivity, refractive index, extinction coefficient, absorption coefficient, real part of optical conductivity and electron energy loss are calculated and their spectra are analyzed. In addition, the band structure, density of states and the bowing parameter of the Zn 2OX (X = S, Se, Te) semiconductors are also obtained and given. The trends in physical properties are also discussed and compared with the available results.

First principles study of electronic and optical properties of zincblende InP

Electronic and optical properties of InP in zincblende crystal structure are studied using the full potential linearized augmented plane wave plus local orbitals (FP-LAPW+lo) program. The complex dielectric function and optical constants, such as optical absorption coefficient, reflectivity, refractive index and extinction coefficient, are calculated, which are in good agreement with the experimental results, better than those from the full potential linear muffin-tin orbital (FP-LMTO) method. We also have explained the origin of the spectral peaks on the basis of the electronic band structures.

Evidence of the correlation between a strong 4d-As/2p-N orbitals coupling and the bowing effect in GaAsN

By means of a simple physical argumentation, we found that the giant bowing observed in GaAsN is correlated to the interaction between 4d-As and 2p-N orbitals. The calculations were carried out within the first principles full potential linear muffin-tin orbitals (FPLMTO) method in its plane wave approximation (PLW) which enables an accurate treatment of the interstitial regions. The choice of this method ensures our work to be free from adjustable parameters and enabled us to perform a microscopic study.

Study of the Fermi Surface ofZrB12Using the de Haas-van Alphen Effect

The de Haas-van Alphen (dHvA) effect in the cluster superconductor ZrB12 was studied by magnetic torque measurements in magnetic fields up to 28 T at temperatures down to 0.07 K. The dHvA oscillations due to orbits from the neck sections and "cubic box" of the Fermi surface were detected. The dHvA frequencies as well as the cyclotron effective masses were calculated using the full-potential linear muffin-tin orbitals method within the generalized gradient approximation. A comparison of the experimental and calculated cyclotron mass shows unusually large electron-phonon interaction on the neck (lambdaep=0.95) and box (lambdaep=1.07) sections of the Fermi surface on the Brillouin zone boundaries.

Structural and electronic properties of LaN

Using two different first principle methods, the full potential linear augmented plane waves (FPLAPW) and a version of the full potential linear muffin-tin orbitals method (FPLMTO) which enables an accurate treatment of the interstitial regions, the structural properties of LaN are investigated. It predicts the possibility of an additional local minimum in the wurtzite (B4) phase, approximately like ScN and YN for which a second minimum for the hexagonal A3 phase was found. A competition between the rocksalt (B1) and the wurtzite (B4) as the ground state phase is found depending on whether LDA (local density approximation) or GGA (generalized gradient approximation) is used. The electronic properties are also discussed.

Structural and electronic properties of GaAsBi

The structural and electronic properties of the GaAs 1− x Bi x ternary alloy are investigated by means of two first principles and full potential methods, the linear augmented plane waves (FPLAPW) method and a recent version of the full potential linear muffin-tin orbitals method (FPLMTO) which enables an accurate treatment of the interstitial regions. In particular, we have found that the maximal GaBi mole fraction x for which GaBi x As 1− x remains a semiconductor is probably around x = 0.5 . The electronic properties of (GaAs) m /(GaBi) n quantum well superlattices (SLs) have also been calculated and it is found that such SLs are semiconductors when m is larger or equal to n .

First-principle calculations of elastic and electronic properties of the filled skutterudite CeFe4P12

A theoretical study of elastic and electronic properties of the filled skutterudite CeFe4P12 is presented, using the full-potential linear muffin–tin orbital (FP-LMTO) method. In this approach the local spin density approximation (LSDA) was used for the exchange-correlation (XC) potential. Results are given for lattice constant, bulk modulus, its pressure derivative and elastic constants. Our calculations performed for band structure and density of state show that this compound is an indirect band gap material (Γ–N). The results are compared with previous calculations and experimental data.

Linear response results for phonons and electron–phonon coupling in hexagonal closepacked Sc-spin fluctuations, and implications for superconductivity

We present a FP-LMTO (full-potential linear muffin-tin orbital) study of the variation inthe electronic structure, phonon frequencies and electron–phonon coupling in hexagonalclose packed (hcp) Sc under pressure. The electron–phonon coupling constantλ is found to increase steadily with pressure in the hcp phase, until the pressure reaches a valuewhere the hcp phase becomes unstable. Linear response calculations for the normal pressurec/a ratio predict a phase change somewhere between calculated pressures of 22 and 30 GPa.The calculated frequencies for the equilibrium hcp lattice parameters are in goodagreement with the inelastic neutron scattering results. There is a small upward shift in theΓ-pointE2g mode frequency under pressure, in qualitative agreement with the Raman spectroscopystudy of Olijnyk et al (2006 J. Phys.: Condens. Matter 18 10971). From the measured valueof the electronic specific heat constant and the calculated values of the Fermi leveldensity of states and electron–phonon coupling constant, we conclude that theelectron–paramagnon coupling constant in hcp Sc should be comparable to theelectron–phonon coupling constant. This indicates that the spin fluctuation effects arestrong enough to suppress superconductivity completely in hcp Sc. We argue that spinfluctuations should be reduced by a factor of two or more in the high pressure Sc-II phase.On the basis of estimates of the electron–paramagnon coupling constants and thecalculated or estimated electron–phonon coupling constants, we argue that thehcp phase may become superconducting with a very low transition temperatureimmediately prior to the transition to the Sc-II phase and that the Sc-II phaseshould indeed be superconducting. The electronic, electron–phonon and spinfluctuation properties of hcp Sc under pressure are compared with those of the highpressure hcp phase of Fe, which was reported to be superconducting a few yearsback.

Structural and electronic properties of bulk YN and of the YN/ScN superlattice

The structural and electronic properties of YN are investigated using two different first principles’ methods: the full potential linear augmented plane waves (FPLAPW) method and a recent version of the first principles full potential linear muffin-tin orbitals (FPLMTO) method which enables an accurate treatment of the interstitial regions. Our calculations show that the ground state configuration of YN is the rocksalt (B1) structure and that it is a semiconductor. We have also investigated the A3 hexagonal structure which is nearly five-times coordinated and found it more stable than the previous wurtzite phase. So that we confirm the presence of another local minimum but in this A3 phase and not in the wurtzite (B4). Nevertheless, the transition from rocksalt (B1) to CsCl (B2) structure is found to be possible at high pressure. The zinc blende structure (B3) has also been investigated and is found to have a large and direct fundamental gap. The resemblances between YN and ScN and their small lattice mismatch led us to perform predictive investigations on rocksalt/rocksalt ScN/YN heterostructure superlattices. The latter shows interesting features. These systems constituted from indirect bandgap bulk materials are found to have a direct bandgap suggesting that the reason is probably the zone folding phenomenon which is suspected to be at the origin of a similar effect observed in the popular Si/SiGe systems. To our knowledge, rocksalt/rocksalt superlattice systems have not received particular attention before.

Effect of lithium concentration on the thermal and optical properties ofLixMn2O4by photoacoustic measurements

In the present work, pellets of ${\mathrm{Li}}_{x}{\mathrm{Mn}}_{2}{\mathrm{O}}_{4}$ polycrystalline powder samples with $x=0.8$, 0.9, 1.0, 1.1, and 1.2 are analyzed to understand the effect of lithium concentration on the thermal and optical properties, and the electronic structure of ${\mathrm{Li}}_{x}{\mathrm{Mn}}_{2}{\mathrm{O}}_{4}$ predicted in an earlier work using full-potential linear muffin-tin orbital (FP-LMTO) method is experimentally verified. The experimental tool used for the determination of the thermal and optical properties is the well-known photoacoustic technique. The variation of thermal diffusivity with changing $x$ values in ${\mathrm{Li}}_{x}{\mathrm{Mn}}_{2}{\mathrm{O}}_{4}$ is extensively studied to explain the influence of lithium concentration on the thermal properties, and has been correlated with the structural asymmetry and defects in ${\mathrm{Li}}_{x}{\mathrm{Mn}}_{2}{\mathrm{O}}_{4}$. The optical absorption spectrum, being the signature of the electronic structure of materials, is recorded in the visible range $(350--800\phantom{\rule{0.3em}{0ex}}\mathrm{nm})$. Six prominent absorption peaks associated with the $\mathrm{O}\phantom{\rule{0.2em}{0ex}}2p\text{\ensuremath{-}}\mathrm{Mn}\phantom{\rule{0.2em}{0ex}}{t}_{2g}$, $\mathrm{O}\phantom{\rule{0.2em}{0ex}}2p\text{\ensuremath{-}}\mathrm{Mn}\phantom{\rule{0.2em}{0ex}}{e}_{g}$, and $\mathrm{Mn}\phantom{\rule{0.2em}{0ex}}{t}_{2g}\text{\ensuremath{-}}\mathrm{Mn}\phantom{\rule{0.2em}{0ex}}{e}_{g}$ band transitions for ${\mathrm{Li}}_{x}{\mathrm{Mn}}_{2}{\mathrm{O}}_{4}$, with $x\ensuremath{\leqslant}1$, are observed experimentally, substantiating the electronic structure predicted by the FP-LMTO method. However, it is observed that there are more absorption peaks in the case of ${\mathrm{Li}}_{1.1}{\mathrm{Mn}}_{2}{\mathrm{O}}_{4}$ and ${\mathrm{Li}}_{1.2}{\mathrm{Mn}}_{2}{\mathrm{O}}_{4}$, which is attributed to the structural distortion from pure cubic spinel structure to a mixture of spinel and tetragonal structures, which is verified by the x-ray diffraction spectra.

Electronic structure and diffusion paths of Ag ions in rocksalt structured AgI

The electronic structure and diffusion paths of Ag ions in the rocksalt structured phase of AgI (rs-AgI) are studied based on the full-potential linear-muffin-tin-orbital (FP-LMTO) method. Ag ions in the rs-AgI start to migrate along the 〈111〉 direction due to the low energy barrier, as is well known in the cases of AgBr and AgCl. The high ionic conductivity in rs-AgI might be expected from the viewpoint of the empirical overlap parameters between Ag 4d electrons and halogen p electrons.

Thermodynamic properties of Cu under high pressure

The total energies, structural properties and elastic constants of Cu at T=0 k have been calculated by the full-potential linearized muffin-tin orbital (FP-LMTO) scheme within the generalized gradient approximation (GGA) correction in the frame of density functional theory. Through the quasi-harmonic Debye model, in which the phononic effects are considered, the dependences of relative volume V/ V 0 on pressure P, cell volume V on temperature T, linear thermal expansion on temperature and Debye temperature Θ and specific heat C V on pressure are successfully obtained. The obtained pressure dependence of the normalized volume at 300 K is in excellent agreement with the experimental results.