S. M. Mujibur Rahman

Atomic transport properties of AgIn liquid binary alloys

The atomic transport properties namely the diffusion coefficient and shear viscosity of less-simple liquid binary alloys, AgIn, are investigated by using the distribution function method. The interionic interaction is modeled by a local pseudopotential. The soft part contribution of the potential to the viscosity involves an integration. The relevant integrand becomes divergent although the derivatives of the potential as well as the pair distribution function individually converge. Thus a truncation of the integrand is required for numerical calculation. The effect of different truncation position on the viscosity is examined thoroughly. An effective truncation procedure is proposed. Results show that the hard part contribution of the potential is dominant for the concerned systems.

Liquid state structure of some noble and transition metals

The static structure factors, S(q), for a number of liquid noble and transition metals are calculated. The underlying theory combines together a simple form of the N-body potential and the thermodynamically self-consistent variational modified hypernetted chain (VMHNC) theory of liquid. The static structure factors calculated by using the VMHNC resemble the hard sphere (HS) and these are consistent with experiments.

Electronic Transport Properties of Liquid Less-Simple Metals

Electronic transport properties, namely the electrical resistivity and the thermoelectric power, of liquid less-simple metals, Zn, Cd, Hg, In, Tl, Sn, Pb, Sb, and Bi, are calculated using Zimans theory. The effective electron-ion and ion-ion interactions are described by the Bretonnet-Silbert model. The static structure factors are evaluated by the self-consistent Variational Modified Hyper-netted Chain (VMHNC) integral equation of liquids. The results for the electrical resistivity are fairly good when compared with experimental data, but the agreement improves significantly when the blurring of the Fermi surface due to the finite electron mean free path is accounted for. The values of the thermoelectric power, for most systems, have the same sign and order of magnitude as the experimental ones. The results for the thermopower also show that the contribution of the energy dependent term of the electron-ion potential is significant for the concerned systems.

Concentration dependence of the free energy and other thermodynamic properties of liquid brasses

The concentration behaviour of the various contributions to the Helmholtz free energy and certain other thermodynamic properties in the liquid CuZn, CuAl and CuSn systems are investigated using a formalism based on the pseudopotential perturbation theory and the Gibbs-Bogoliubov inequality.

On the structural stability of metallic glasses

We discuss the various possibilities advanced to account for the structural stability of metallic glasses. Using a formalism based on the pseudopotential theory and the Gibbs-Bogoliubov inequality we calculate the free energies and free energies of formation for the glassy phase of MgCa at various concentrations and compare these results with those for the corresponding solid and liquid phases of the same system. Subsequently, we attempt to explain the stability of the metallic glasses by noting a matching between the positions of the first peakqm in the relevant structure factor and the maximumqs in the relevant screened pseudopotential.

Spin treatment-based approach for electronic transport in paramagnetic liquid transition metals

A novel concept is proposed to calculate both the electrical resistivity and thermoelectric power (TEP) of liquid transition metals (Mn, Fe, Co and Ni) characterized by a paramagnetic state in the liquid phase. By contrast to a previous work (PRB64, 094202 (2001)), where the resistivity was calculated by treating separately the interactions between spin up and spin down using the Matthiessen rule, our current approach is based on two types of muffin tin potentials in the t-matrix, namely spin up and spin down. The resistivity is treated as the result of the interference of the two kinds of spin states of electrons including a cross-contribution. The calculated resistivity values agree reasonably well with the available experimental ones for all the metals considered. Moreover, the calculated TEP, as deduced from the slope of resistivity vs. energy, has been found to be positive for Mn and Fe but negative for Co and Ni. Besides that, this formalism for resistivity calculation may be generalized to a system that may exist in different atomic states. It is worth mentioning that this concept is analogous to the one used in the process of neutron scattering on a metal composed of multiple isotopes.

Structural, thermodynamic and transport properties of liquid noble and transition metals

Abstract We have investigated a number of structural, thermodynamic and atomic transport properties of various liquid noble and transition metals. The underlying theory combines a simple form of the N-body potential and the thermodynamically self-consistent variational modified hypernetted chain (VMHNC) theory of liquid. The static structure factors calculated by using the VMHNC resemble, as expected, the hard sphere (HS) values. Consequently the HS model is used to calculate thermodynamic properties, viz. the specific heat, entropy, isothermal compressibility and the shear viscosity of liquid Ni, Cu, Ag, and Au. The results are in reasonable accord with the experimental values.

Calculations of g(r) for liquid Cu and Ni using many-body potentials

Abstract The pair distribution function, g(r), for Ni and Cu at various temperatures above melting are investigated by using the Finnis-Sinclair (FS) many-body potentials and the thermodynamically self-consistent Variational Modified Hypernetted Chain (VMHNC) theory. The overall agreement with experiment is reasonably good. The calculations indicate that the many-body interactions, precisely taken care of by the FS potentials, are important for the study of g(r) for the liquid transition and noble metals. The results also permit us to examine the applicability of the temperature independent approximation of the FS potentials.

Electron transport in liquid silicon and germanium

Abstract We report on the electrical resistivity and thermoelectric power of liquid Si and Ge. The basic ingredients of the calculations are obtained by using a variational procedure based on a third-order perturbation theory. In the calculations we employ an on-Fermi-sphere model potential suitable for these systems. The reference structure factors used in the final calculations are obtained by introducing softness in the hard-sphere description of the structure factors through a scaling procedure. The calculated resistivities and thermoelectric power are comparable to the experimental as well as to the available theoretical results.

PHASE STABILITY OF ALKALI METALS UNDER PRESSURE: PERTURBATIVE AND NON-PERTURBATIVE TREATMENTS

We have investigated the structural phase stability of crystalline alkali metals under external pressure in terms of their pair potentials, structural free energies, thermomechanical properties viz. the elastic constants and the density-of-sates [DOS] at the Fermi level. The pair potentials are calculated using amenable model potentials, the structural energies and the elastic constants are calculated in terms of the effective pair potentials and the DOS for the systems are calculated by employing the augmented-spherical-waves [ASW] method. The matching between the minima of the pair potentials and the relative positions of the first few lattice vectors of the relevant structures gives a qualitative impression on the relative stability of a crystal phase. Similarly the appearance of a minimum in the energy difference curves between relevant crystal structures manifests a relatively stable structure. On the contrary, a maximum in the bulk modulus indicates a stable structure; these maximum-minimum criteria are controlled by the profile of the effective pair interactions of the constituent atoms. If the relevant lattice vectors are populated in and around the minimum of the respective pair potential the corresponding bulk modulus shows a maximum trend. The same situation gives rise to a minimum in the free energy. Both of these tendencies favor a particular crystalline phase against other relevant structures. Similarly a maximum in the DOS curves gives rise to a minimum in the energy curve manifesting a stable structure. The population of electronic states plays the responsible role here. To treat the two entirely different methods, namely, the perturbative pseudopotential theory and the non-perturbative ASW method on the same footing, we have used the same metallic density in both the methods for the respective element. The calculated results show a qualitative trend in support of the observed structures for these elemental systems.