Full-potential Linear Muffin-tin Orbital Method Research Articles

Physical Properties of the Zn<sub>x</sub>Cd<sub>1-x </sub>Se Alloys: Ab-Initio Method

The present work performs self-consistent ab initio full-potential linear muffin-tin orbital (FP-LMTO) method to study the structural and electronic properties of the ternary ZnxCd1-xSe alloy, based on density functional theory (DFT). In this approach, both the local density approximation (LDA) and the generalized gradient approximation (GGA) were used for the exchange-correlation potential calculation. The ground-state properties are determined for the bulk materials CdSe, ZnSe and their alloy in cubic phase. In particular, the lattice constant, bulk modulus, electronic band structures and effective mass. We mainly showed deviation of the lattice parameter and bulk modulus from Vegard’s law of our alloys. We also presented the microscopic origins of the gap bowing using the approach of Zunger et al. The results are compared with other theoretical calculations and experimental data and are in reasonable agreement.

Theoretical investigation of the elastic, thermodynamic, electronic and magnetic properties of PrNi 2Si 2 and PrNi 2Ge 2

The structural, elastic, thermodynamic, electronic and magnetic properties of ferromagnetic tetragonal PrNi 2Si 2 and PrNi 2Ge 2 compounds have been calculated using the full-potential linear muffin-tin orbital (FP-LMTO) method. The exchange–correlation potential is treated within the local spin density approximation of Perdew and Wang (LSDA–PW). Moreover, we have added the Coulomb interaction U to improve the electronic band structure calculations and the magnetic properties. The calculated structural parameters are in good agreement with the experimental data. The elastic constants C ij are predicted using the total energy variation versus strain technique. The polycrystalline elastic moduli, namely; shear modulus, Young’s modulus, Poisson’s ratio, sound velocities and Debye temperature are derived from the obtained single-crystal elastic constants. Ductility behavior of these compounds is interpreted via the calculated elastic constants C ij . Electronic and bonding properties are discussed from the calculations of band structure and density of states. The thermodynamic properties are predicted through the quasi-harmonic Debye model, in which the lattice vibrations are taken into account. The variation of the bulk modulus, lattice constant, heat capacities and Debye temperature with pressure and temperature are successfully obtained.

Structural properties and new phase transitions of ScN using FP-LMTO method

By full potential linear muffin-tin orbitals (FP-LMTO) method, we have studied the phase transitions of ScN under high pressures. The local density (LDA) approximation was used for the exchange and correlation energy density functional. The most important result is the prediction of the possibility of two phase transitions from the cubic rocksalt (NaCl) structure to the orthorhombic CaSi (Cmmc) structure above 252.5 GPa and to the tetragonal AuCu (P4/mmm) structure at 303.017 GPa, the first one (NaCl–CaSi) occurring at a lower pressure than the well known NaCl to CsCl transition (found here to be 324 GPa).

Simulation of absorption of femtosecond laser pulses in solid-density copper

We present a simulation of absorption of femtosecond laser pulses by a copper target. The modeling involved thermodynamic functions calculated by using a first-principles full-potential linear muffin-tin orbital method and chemical-picture-based model of dense plasma utilizing a superconfiguration approach. The results of the simulation are compared to experimental and other theoretical data. The role of the electron-ion energy exchange is analyzed and further work on detailed improvement of the presented theoretical model is discussed.

High-pressure structural study of yttrium monochalcogenides from experiment and theory

High-pressure powder x-ray diffraction experiments using synchrotron radiation are performed on the yttrium monochalcogenides YS, YSe, and YTe up to a maximum pressure of 23 GPa. The ambient NaCl structure is stable throughout the pressure range covered. The bulk moduli are determined to be 93, 82, and 67 GPa for YS, YSe, and YTe, respectively. First-principles total energy calculations are carried out using the full-potential linear muffin-tin orbital method. The calculated and measured lattice constants and bulk moduli are in good agrement. Under applied pressure, the yttrium monochalcogenides are predicted to undergo a structural transition. Assuming that the high-pressure phase corresponds to the CsCl crystal structure, transition pressures of 53, 36, and 14 GPa are found for YS, YSe, and YTe, respectively.

FIRST-PRINCIPLES HIGH-PRESSURE ELASTIC AND THERMODYNAMIC PROPERTIES OF TANTALUM

The all-electron full-potential linearized muffin-tin orbital method, by means of quasi-harmonic Debye model, is applied to investigate the elastic constant and thermodynamic properties of body-centered-cubic tantalum (bcc Ta). The calculated elastic constants of bcc Ta at 0 K is consistent with the previous experimental and theoretical results. Our calculations give the correct trends for the pressure dependence of elastic constants. By using the convenient quasi-harmonic Debye model, we refined the thermal equations of state. The thermal expansivity and some other thermal properties agree well with the previous experimental and theoretical results.

FIRST PRINCIPLES STUDY OF THE STRUCTURAL, ELASTIC AND ELECTRONIC PROPERTIES OF Ti2InC and Ti2InN

The structural, elastic and electronic properties of Ti 2 InC and Ti 2 InN compounds have been calculated using the full-potential linear muffin-tin orbital (FP-LMTO) method. The exchange and correlation potential is treated by the local density approximation (LDA). The calculated ground state properties, including, lattice constants, internal parameters, bulk modulus and the pressure derivative of the bulk modulus are in reasonable agreement with the available data. The effect of pressure, up to 40 GPa, on the lattice constants and the internal parameters is also investigated. Using the total energy-strain technique, we have determined the elastic constants Cij, which have not been measured yet. The band structure and the density of states (DOS) show that both materials have a metallic character and Ti 2 InN is more conducting than Ti 2 InC . The analysis of the site and momentum projected densities shows that the bonding is achieved through a hybridization of Ti -atom d states with C ( N )-atom p states. Otherwise, it has been shown that Ti – C and Ti – N bonds are stronger than Ti – In bonds.

Study of structural, elastic and electronic properties of GdX (X = Bi, Sb) compounds using LSDA and LSDA + U approach

In order to study the structural, and elastic properties of GdX (X=Bi, Sb), we employ all-electron full-potential linearized muffin-tin orbital method (FP-LMTO) within the frame of density functional theory (DFT). The exchange correlation energy is described in the local spin density approximation LSDA using the Perdew–Wang parameterization. The equilibrium lattice parameters, bulk modulus, transition pressure, elastic constants and their related parameters such as Poisson’s ratio, Young modulus, shear modulus and Debye temperature were calculated.We compared our obtained results with available experimental and theoretical data. They are in reasonable agreement. In this paper the electronic properties are treated with LSDA+U approach. Our results show that both compounds exhibit a semi metallic behavior.

First-principles Study of Nitrogen Vacancies in GdN

ABSTRACTThe electronic structure of nitrogen vacancies in gadolinium nitride are studied using the full-potential linearized muffin-tin orbital method in the local spin density approximation with Hubbard U corrections (LSDA+U). The vacancy is found to have two localized defect levels in the gap, one of each spin. The third electron of each vacancy in the neutral state dopes the conduction band. The single positive state is found to be the ground state for Fermi levels located anywhere within the band gap. The vacancy has a net magnetic moment of 1 μB in the neutral charge state. The presence of the vacancy is found to increase the average exchange interactions between Gd atoms and hence the Curie temperature but only by about a factor 2 compared to GdN without vacancies.

Site Dependence of Electronic Structure of Gd Impurities in GaN

ABSTRACTElectronic structure calculations are reported for Gd in GaN on Ga as well as on N site and for pairs of Gd on neighboring Ga and N sites, using the full-potential linearized muffin-tin orbital method in the local spin density approximation with Hubbard U corrections (LSDA+U). The energy of formation for the N site is found to be much higher than for the Ga site even after relaxations are included. The GdN configuration is found to be at best metastable (in ZB). In WZ and in the pair configurations, the Gd is found to move toward an interstitial site leaving a nitrogen vacancy behind. The electronic structure of these structures and their magnetic moments are discussed.

High-pressure structural study of fluoro-perovskiteCsCdF3up to 60 GPa: A combined experimental and theoretical study

The structural behaviour of CsCdF3 under pressure is investigated by means of theory and experiment. High-pressure powder x-ray diffraction experiments were performed up to a maximum pressure of 60 GPa using synchrotron radiation. The cubic $Pm\bar{3}m$ crystal symmetry persists throughout this pressure range. Theoretical calculations were carried out using the full-potential linear muffin-tin orbital method within the local density approximation and the generalized gradient approximation for exchange and correlation effects. The calculated ground state properties -- the equilibrium lattice constant, bulk modulus and elastic constants -- are in good agreement with experimental results. Under ambient conditions, CsCdF3 is an indirect gap insulator with the gap increasing under pressure.

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.

First-principles study of structural, electronic and elastic properties under pressure of calcium chalcogenides

We present ab initio calculations for CaS, CaSe and CaTe, in the B1 (NaCl) and B2 (CsCl) phase, by means of accurate first principle total energy calculations using the all-electron full-potential linear muffin-tin orbital method FP-LMTO.The calculations are presented within the local density approximation (LDA). Results are given for structural, electronic and elastic. Good agreement is found with experimental data. The efficiency and the accuracy of this method are so appreciated to predict some properties of this kind of materials.

Prediction study of the structural, elastic, electronic and optical properties of the antiperovskite [formula omitted

We use an ab initio full-potential linear muffin-tin orbital method within the local density approximation (LDA) to study the structural, elastic, electronic and optical properties of the antiperovskite BiNBa 3. The calculated lattice parameter is in good agreement with previous calculations. The elastic constants and their pressure dependence are calculated; we found a linear dependence of elastic stiffness on the pressure. We estimated the Debye temperature of this compound from the average sound velocity. We also present results of the effective masses for the electrons in the conduction band (CB) and the holes in the valence band (VB). To complete the fundamental characteristics of this compound we have analyzed the optical properties.

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.

Multiplet effects in the electronic structure of intermediate-valence compounds

We present an implementation of the Hubbard-I approximation based on the exact solution of the atomic many-body problem incorporated in a full-potential linear muffin-tin orbital method of density- ...

Vibrational properties of rare-earth nitrides: Raman spectra and theory

Raman spectra are presented for the rare-earth nitrides SmN, GdN, DyN, ErN, and LuN measured with 633 and 514 nm excitation wavelengths and at temperatures above and below the Curie temperature. Frozen-phonon calculations are presented for the phonons at Gamma, L, and X points in the same series of materials plus previously studied YbN using the full-potential linearized muffin-tin orbital method and the LSDA+U (local spin-density approximation+Hubbard U corrections). The method is found to be in good agreement with recent linear-response pseudopotential calculations for the closely related ScN. Comparison with ScN and Eu chalcogenides (EuS, EuO) allows us to conclude that the main spectral line seen in the RE-N is a disorder induced phonon density of states like spectrum heavily weighted by the LO(L) modes. Its second harmonic 2LO(L) is also observed. The increasing frequency trend with atomic number is related to the decreasing trend in lattice constant and hence increase in force constant rather than the mass of the rare-earth ion because this phonon mode is purely a N-vibrational mode. The disorder does not arise from the spin orientations because no changes are observed upon magnetic ordering but may arise from point defects and the size of the crystallites.

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.

First Principles Investigation of Ferromagnetism for Zn1-xMnxY(Y = S, Se, Te)

Through first-principles full-potential linear muffin-tin orbital (FP-LMTO) method within the local density approximation, we investigate the structural and electronic properties of Zn1-xMnx Y (VIa) where Y represent an element of the VIa column(S, Se and Te) compounds-based diluted magnetic semiconductors (DMS) in the Zinc-blend structure. We have investigated the lattice parameters and band gap energies. The lattice constants a are found to change linearly for the Zn1-xMnxTe and Zn1-xMnxS alloy

Electronic structure and magnetism inBi2Te3,Bi2Se3, andSb2Te3doped with transition metals (Ti–Zn)

A less studied class of magnetic semiconductors based on the tetradymite structure compounds, which include ${\text{Bi}}_{2}{\text{Te}}_{3}$, ${\text{Bi}}_{2}{\text{Se}}_{3}$, and ${\text{Sb}}_{2}{\text{Te}}_{3}$, doped with $3d$ transition-metal $(T)$ elements is investigated using the full-potential linearized muffin-tin orbital method in the local spin-density approximation (LSDA). The small size of the $T$ atoms (Ti\char21{}Zn) relative to the larger Bi/Sb atom site leads to a strong lattice relaxation, which primarily affects the atoms close to the defect in neighboring layers but has less impact within the layer containing the $T$ ion. Even with the relaxation, the size difference leads to quite localized $3d$ states and hence a high-spin state with large magnetic moments. The valence is $3+$ for the first half of the series but reduces closer to $2+$ (Co) or $1+$ (Ni) for the latter half of the series. This reduction is due to hybridization in the transition-metal $3d$ state with the $\text{Se}/\text{Te}\text{ }p$ state of the atom in the layer closest to the $T$ site which reduces the amount of charge transfer between these two atoms. It corresponds to a competition between the stabilization by the exchange energy dominating for the early $T$ ions and the covalent bonding effects for the later ones. For Cu and Zn the trend reverses and the valency is between $2+$ and $3+$ with a small magnetic moment remaining for Cu but a negligible moment for Zn. $\text{LSDA}+U$ calculations for the Fe-Ni atoms slightly change this balance of the two effects and promote higher valency and larger magnetic moment.