The structure of a melt: The case of liquid bismuth

Abstract

Molecular Dynamics (MD) is performed on supercells of 216 atoms of bismuth, going from 300 K to 573 K in 100 steps and maintaining it in the liquid state, at 573 K, during 500 steps using the Materials Studio (MS) suite of codes. The Pair Distribution Functions (PDFs) and the Plane Angle Distributions (PADs) of the last 1, 10, 25 and 100 steps of the MD have been obtained. Averaging the last 100 steps, as representative of the liquid, Reverse Monte Carlo (RMC) was applied to obtain 4 atomic structures, one for each set of initial random velocities. Then, a detailed structural study of liquid bismuth at 573 K was undertaken; PDFs and PADs are calculated and reported. Two noticeable peaks appear for the PDFs, at 3.25 and 6.55 Å, along with a pseudo peak (shoulder) at 4.6 Å. This shoulder (after the first peak) of the PDFs is found to be related to the third and fourth neighbor peaks of the crystalline Wyckoff structure and also to the diagonal distances in deformed squares in the liquid structure. For completeness J(r)s are also reported. Two prominent peaks in the MS PADs are observed: 53° and 85°; and two for the RMC PADs: 58° and 90°, suggesting the existence of deformed triangles and squares. Less abundant are higher-order geometrical structures.