Orbital free ab initio molecular dynamics simulation study of some static and dynamic properties of liquid noble metals

Bhuiyan Bhuiyan,L.E González,D.J González

doi:10.5488/cmp.15.33604

Abstract

Several static and dynamic properties of liquid Cu, Ag and Au at thermodynamic states near their respective melting points, have been evaluated by means of the orbital free ab-initio molecular dynamics simulation method. The calculated static structure shows good agreement with the available X-ray and neutron diffraction data. As for the dynamic properties, the calculated dynamic structure factors point to the existence of collective density excitations along with a positive dispersion for l-Cu and l-Ag. Several transport coefficients have been obtained which show a reasonable agreement with the available experimental data.

Highlights

The d-electrons in the d-band metals are not so free as to justify a nearly free electron (NFE) approach but, on the other hand, they are not so tightly bound as to be described by the tight binding method (TBM) or core electron theory
OF-ab-initio molecular dynamics (AIMD) simulations have been performed for l–Cu, l–Ag and l–Au at two thermodynamic states near their respective triple points
The average number of nearest neighbors, known as coordination number (CN), is obtained by integrating the radial distribution function (RDF), 4πr 2ρg (r ), up to a distance rm which is usually identified as the position of the first minimum in either the RDF or the g (r ) [67, 68]. Both choices often lead to rather similar results and in what follows we report the results obtained by integrating up to the first minimum of the RDF which was found at rm ≈ 3.42 and 3.44 Å for T = 1443 and 1773 K, leading to values CN ≈ 12.9 and 12.6, respectively

Summary

Introduction

The d-electrons in the d-band metals are not so free as to justify a nearly free electron (NFE) approach but, on the other hand, they are not so tightly bound as to be described by the tight binding method (TBM) or core electron theory. Bogicevic et al [35] used the effective medium theory to obtain a many-body potential which, combined with CMD simulations, provided information on the static properties and the self-diffusion coefficient of l–Au at different temperatures Their calculated pair distribution function, g (r ), near melting has the main peak which is somewhat lower than experiment and the subsequent oscillations are slightly out of phase. Pasturel et al [49], within a wider study of Au–Si alloys, performed AIMD simulations of liquid and undercooled Au, using 256 atoms and equilibrium runs 6 ps long, and obtained results for the temperature variation of the self-diffusion coefficient and icosahedral atomic arrangements None of these AIMD calculations produced results for the dynamical properties, because its evaluation requires in general larger systems, and, in particular, substantially longer simulation times.

Theory

Results and discussion

Liquid Cu

Dynamic properties

Liquid Au

Conclusion