A. R. Jani

The temperature-dependent electrical transport properties of liquid Sn using pseudopotential theory

We present the calculations of electrical resistivity, thermo-electric power and thermal conductivity based on the self-consistent approximation. The pseudopotential due to Hasegawa et al. [J. Non-Cryst. Solids 117/118, 300 (1990)] for full electron–ion interaction, which is valid for all electrons and contains the repulsive delta function to achieve the necessary s-pseudisation, was used in the calculation. Temperature dependence of structure factor is achieved through temperature-dependent potential parameter in the pair-potential. The outcome of the present study is discussed in the light of other such results and with predictions of Wiedemann and Franz law up to moderately high temperature. Specially, high-temperature resistivity data necessitates the careful investigation of electron energy dispersion close to the Fermi level and possible metal to non-metal transition while going from dense-fluid to low density-fluid state. In the absence of experimental data at high temperature, these findings may serve as future guideline.

Thermodynamic properties of 3C SiC

In the present paper, we report on the results of various thermodynamic properties of 3C‐SiC at high pressure and temperature using first principles calculations. We use the plane-wave pseudopotential density functional theory as implemented in Quantum ESPRESSO code for calculating various cohesive properties in ambient condition. Further, ionic motion at a finite temperature is taken into account using the quasiharmonic Debye model. The calculated thermodynamic properties, phonon dispersion curves, and phonon densities of states at different temperatures and structural phase transitions at high pressures are found to be in good agreement with experimental and other theoretical results.

Collective Modes and Elastic Constants of Liquid Al83Cu17 Binary Alloy

The collective dynamics (longitudinal and transverse phonon modes) are studied for aluminum-copper (Al-Cu) binary alloy in terms of the eigen-frequencies of the localized collective excitations. The model pseudopotential formalism is employed using a self-consistent phonon scheme by involving multiple scattering and phonon eigen-frequencies. These frequencies are expressed in terms of many-body correlation functions of atoms as well as of interatomic potential. The important ingredients in the present study are the pair-potential and pair-correlation functions. The most recent and sparingly used local field correlation functions are employed to investigate the influence of the screening effects on the vibrational dynamics of non-crystalline Al83Cu17 binary alloy. The results for the elastic constants like bulk modulus BT, rigidity modulus G, Poissons ratio ζ, Youngs modulus Y, Debye temperature θD, propagation velocity of elastic waves and dispersion curves are reported based on the collective modes of this binary alloys. The present results are consistent and confirm the applicability of model potential and self-consistent phonon theory for such studies.

Study of phonon modes and elastic properties of Sc36Al24Co20Y20 and Gd36Al24Co20Y20 rare-earth bulk metallic glasses

A phonon modes and elastic properties of two different rare-earth based bulk metallic glasses Sc36Al24Co20Y20 and Gd36Al24Co20Y20 are computed using Hubbard-Beeby approach and our well established model potential. The local field correlation functions due to Hartree (H), Taylor (T), Ichimaru and Utsumi (IU), Farid et al (F) and Sarkar Sen et al (S) are employed to investigate the influence of the screening effects on the vibrational dynamics of Sc36Al24Co20Y20 and Gd36Al24Co20Y20 bulk metallic glasses. The results for bulk modulus BT, modulus of rigidity G, Poissons ratio ξ, Youngs modulus Y, Debye temperature ΘD, propagation velocity of elastic waves and dispersion curves are reported. The computed elastic properties are found to be in good agreement with experimental and other available data.

Pressure induced Structural Phase Transition in SrS

Pressure induced structural phase transition in SrS from NaCl (B1) structure to CsCl (B2) structure has been studied using plane wave pseudopotential density functional theory as implemented in Quantum Espresso code. Ultrasoft pseudopotential along with generalised gradient approximation (GGA) has been used for total energy calculation. The electronic band structure has been calculated for B1 phase of SrS. We also report the vibrational properties such as phonon frequencies along major symmetry directions using density functional perturbation theory. The phase transition pressure is calculated by comparing enthalpies of both phases and its presently calculated value is 17.95 GPa, in very good agreement with the experimental results.

Effect of pressure on some optical properties of GaxIn1−xP semiconductors

A theoretical procedure is presented for the study of optical properties of ternary alloy GaxIn1−xP. The calculations are based on the pseudopotential formalism in which local potential coupled with the virtual crystal approximation (VCA) is applied to evaluate the effect of pressure on the optical properties like refractive index, electronic polarizability, plasmon energy, dielectric constant and equation of state for gallium concentration x = 0, 0.25, 0.50, 0.75 and 1 of the ternary alloy GaxIn1−xP. To incorporate the screening effect, local field correction functions due to Hartree, Taylor, Ichimaru et al. and Nagy are employed. The refractive index, electronic polarizability and dielectric constant computed for the parent binary compounds GaP and InP are in satisfactory agreement with the experimental report. It is seen that the refractive index of GaxIn1−xP decreases nonlinearly with the increase in pressure. The results obtained using Hartrees screening functions are not very close to the experimental data as it does not include any exchange and correlation effects. Overall good agreement with the experimental and other theoretical findings confirms the application.

Thermal Expansion of Some Fcc Transition Metals

Volume thermal expansion of some fcc transition metals have been studied using improved lattice dynamical model. In this approach, the contribution of s like electron is calculated in 2nd order perturbation theory for the local model pseudopotential (Heine - Abrenkov) while that of the d electrons is taken into account by introduction of repulsive potential. The present study confirms that the use of improved model to study such anharmonic property yields satisfactory results. Looking to the success of present study, the present lattice mechanical model may be used to study thermophysical properties in high temperature and high pressure regions.

Study of Collective Modes and Elastic Constants of Zr57Ti5Cu20Ni8Al10 Bulk Metallic Glass

The methodical expressions for the phonon frequencies of Zr57Ti5Cu20Ni8Al10 bulk metallic glass (BMG) both for longitudinal and transverse phonon modes are computed for the first time using Hubbard-Beeby (HB) approach and our well recognized model potential. The self-consistent phonon scheme given by Takeno-Goda, involving multiple scattering and phonon Eigen frequencies expressed in terms of many-body correlation functions of atoms as well as of interatomic potential in the solids, has been used to generate the collective modes in the Zr57Ti5Cu20Ni8Al10 BMG. In the present paper, the local field correction functions due to Hartree (H), Farid et al (F), Sarkar et al (S) and Hubbard Sham (HS) are used to examine the influence of screening effects on the vibrational properties. Further, from the long wavelength limit of phonon frequencies, various elastic constants have been calculated and are found to be in good agreement with experimental and other available data.

Structure and Electrical Conductivity of Liquid Pb-Bi Alloys

The knowledge of the physical properties of liquid Pb-Bi alloys and those of eutectic composition especially, is of high scientific and practical importance. In present paper temperature dependent electrical conductivity as well as thermoelectric power of liquid Pb-Bi eutectic (Pb-55.9%Bi) is studied in the framework of Ziman formalism through an electron-ion potential. Partial structure factor is calculated from the Faber-Ziman approach. The dependency of conductivity is interpreted alongwith various screening functions. The results are compared with experimental findings and the effect of screening function on conductivity is discussed. This elucidates that the conductivity data of liquid Pb-Bi system are in qualitative agreement with the nearly-free electron picture.

Structural and Vibrational Properties of Manganese Sulfide

Structural properties of MnS have been studied using plane wave pseudopotential density functional theory as implemented in Quantum Espresso code. Local density approximation (LDA) along with ultrasoft pseudopotential has been used for total energy calculations. The calculated total energies are fitted to Murnaghan equation of state to calculate equilibrium lattice constant, isothermal bulk modulus and pressure derivative of isothermal bulk modulus for NaCl-type structure of MnS and compared with previous experimental and theoretical calculations and good agreement is achieved with those results. Phonon frequencies have also been derived for B1 phase of MnS along high symmetry directions using the density functional perturbation theory at ambient condition.