Study of the Bulk Properties of Liquid Transition Metals

Abstract

Due to versatile applications of transition metals it is always interesting to study the properties of these metals and their alloys theoretically. The properties of transition metals largely depend on the electronic configuration of the outermost shell or nextto- outer most shell. We have studied some static and dynamic properties for liquid transition metals by using the orbital free ab initio molecular dynamics (OF-AIMD) simulation technique at thermodynamic states near their respective melting temperatures. The systems studied are the 3d (Cr, Mn, Fe, Co, Ni, Zn), 4d ( Pd, Cd) and 5d (Pt, Hg) liquid transition metals. Due to the availability of experimental data for static structure factor we have also performed simulation at several thermodynamic states for some systems, namely for liquid Fe (l-Fe), l-Zn, l-Hg, and l-Co. The OF-AIMD simulation technique is related to the density functional theory (DFT) of Hohenberg and Kohn. The exchange correlation energy is described by the local density approximation. To describe electron-ion interaction, we have used a model local pseudopotential proposed by Bhuiyan et al., which has proven to be the successful to generate the structural and dynamical properties of some liquid transition metals. The calculated results are presented here for a range of static structural magnitudes, such as static structure factor, isothermal compressibility, pair distribution function and coordination number. A comparison with the available X-ray and neutron diffraction data shows that the OF-AIMD method can provide a reasonable description of the static structure. As for the dynamic properties, results are reported for both single and collective dynamics. The calculated dynamic structure factors show side peaks which point to the existence of collective density excitations, from where the adiabatic sound velocities are calculated. Finally, we have performed calculation of some transport coefficients and obtained results are compared with the corresponding experimental data. Calculated results for static and dynamic properties are found to be good in agreement with available experimental data. We also have observed through the present work that a heavy computational demand of Kohn-Sham orbital representation of DFT used in AIMD can be partly overcomed by the OF-AIMD simulation method.