Investigation of some basic thermodynamic properties of Na-K alloy

Investigation of thermodynamic of liquid binary alloys using pseudopotential theory is reported. The potential suggested by Fiolhais et al. with its individual parameters is used for the entire calculation. A transferability of the potential from the solid to liquid medium is achieved for the presently reported binary alloy. The internal energy components, Helmholtz free energy, entropy, and total energy at various proportions of the participating alkali metals are included in the study. The comparison with the other data has been shown in the present article. Exchange and correlation effect is also tested with the help of various local field correction functions. BIBECHANA 18 (2) (2021) 1-8

Phonon dynamics of Zr67Ni33 AND Fe80B20 binary glassy alloys

Binary amorphous alloys are the primary bulk metallic glasses (BMGs). Two binary BMGs Zr67Ni33 and Fe80B20 have been studied in the present work using the pseudo- alloy-atom (PAA) model based on the pseudopotential theory. Some important thermodynamic properties like Debye temperature and elastic properties like elasticity moduli and Poisson’s ratio at room temperature are theoretically computed with the help of pseudopotential theory from the elastic limit of the phonon dispersion curves (PDCs). The collective dynamics of longitudinal and transverse phonon modes are investigated in terms of eigenfrequencies of the localized collective modes. The presently computed results are compared with the other such data including theoretically generated results from the molecular dynamics at different temperatures as available in the literature and an acceptable agreement is found. BIBECHANA 18 (2021) 33-47

Ising-like models for stacking faults in a free electron metal

We propose an extension of the axial next nearest neighbour Ising (ANNNI) model to a general number of interactions between spins. We apply this to the calculation of stacking fault energies in magnesium—particularly challenging due to the long-ranged screening of the pseudopotential by the free electron gas. We employ both density functional theory (DFT) using highest possible precision, and generalized pseudopotential theory (GPT) in the form of an analytic, long ranged, oscillating pair potential. At the level of first neighbours, the Ising model is reasonably accurate, but higher order terms are required. In fact, our ‘ AN N NI model’ is slow to converge—an inevitable feature of the free electron-like electronic structure. In consequence, the convergence and internal consistency of the AN N NI model is problematic within the most precise implementation of DFT. The GPT shows the convergence and internal consistency of the DFT bandstructure approach with electron temperature, but does not lead to loss of precision. The GPT is as accurate as a full implementation of DFT but carries the additional benefit that damping of the oscillations in the AN N NI model parameters are achieved without entailing error in stacking fault energies. We trace this to the logarithmic singularity of the Lindhard function.

Local minimum in pair potentials of polyvalent metals: A limitation of pseudopotential theory

Local minimum appearing in the interionic pair potentials, when derived from local model pseudopotential, for Al (and some other polyvalent metals) remains as a long standing problem of clear understanding of its origin, although some attempts have been made by a few authors. The origin of this feature of local minimum is systematically investigated for the first time in this paper considering both the core size and the conduction electron density as variables. Interionic pair potential is derived from Ashcroft’s empty core model because it depends on these two variables only. Results of this investigation show monovalent metals do not exhibit a local minimum at all but trivalent Al and some other polyvalent metals do exhibit at their normal densities. Here, the combined effect of the core size and the conduction electron density results whether the local minimum will appear or not. More interestingly, for smaller core size, conduction electron density plays major role and for larger core size the core radius plays the major role in determining the depth of the local minimum.

Elastic Properties of Zr50Cu43Ag7 Bulk Metallic Glass Using Pseudopotential Theory

Using Hubbard-Beeby approach for phonon dynamics, in conjunction with our recently proposed model pseudopotential; phonon frequencies for longitudinal and transverse modes are computed and associated elastic properties of technologically important Zr-based Zr50Cu43Ag7 bulk metallic glass (BMG) are evaluated. Five different forms of the static local field correction functions, viz., Hartree etal. (H), Taylor et al. (T), Ichimaru and Utsumi et al. (IU), Farid et al. (F) and Sarkar et al. (S) are employed to investigate the influence of the screening effect on the vibrational dynamics of Zr50Cu43Ag7 BMG. Results for bulk modulus, modulus of rigidity, Poisson's ratio, Young modulus, propagation velocity of elastic waves and dispersion curves are studied. The theoretical computations are found to be in good agreement with the available experimental results, which confirms the use of our model pseudopotential to study elastic properties of such a glassy system.

Structural Properties of In1-xSnx at Different Concentrations and Temperatures

The partial structure factors for liquid alloy In1-xSnx have been computed at varying concentration and temperatures using pseudopotential theory. The structure factor S(q) and pair correlation function g (r) have been determined using the hard-sphere approximation. The temperature dependent hard-sphere diameter σ (T) is estimated using Vσ=Vminr+12kBT criterion from the computed pair potential. The modified empty-core local pseudopotential, which represents the orthogonalisation effect due to s-core states, is used for electron–ion interaction with proper screening function. The only potential parameter, the core radius, is determined at different temperatures from the knowledge of structure factor. Intrinsic temperature effects have been studied through dimensionless damping term (see formula in paper) in the pair potential. The effect of temperature and concentration on structure factors is discussed to shed light on bonding in technologically important alloy. This used pseudopotential proved successful in explaining the structural properties of non-crystalline alloys at higher temperatures.