First principles molecular dynamics simulation: An electron in non-local pseudopotential; electrons in molten alkali-alkali halide solutions

Abstract

This study presents an ab-initio method based on the Discretized Path Integral Molecular Dynamics (DPIMD) to simulate the electronic behavior in the following systems: (a) an electron in the field of sodium ion, and (b) multi-electron solvation in molten KCl at 1300 K. For the first system, a non-local pseudopotential was incorporated in the path integral derivation of the quantum amplitude. The resulting formalism was then implemented in a molecular dynamics simulation of an electron in the field of sodium ion. The obtained amplitude for the electronic states considered, namely 3s and 3p, came to an excellent agreement with previous computational findings based on Coreless Hartree-Fock method carried by Melius and Goddard III (53). For the second system, the solvation of four, six, and eight electrons in molten KCl, at 1300 K, was studied. In this case a successful incorporation of exchange in DPIMD was made. Bipolarons were formed in each case. However, their electronic charge distribution ranged from two bipolarons with some common charge region, to an elongated structure that stretched over the entire allowed range of interaction. In each case, the size of the bipolaron was found to be ∼4 Å. In this aspect of the study, the results came to an excellent agreement with those of Parrinello and Rahman (9), Fois et al (71), and Selloni et al (72). Apparent in the results of this study is the independence of the local ionic structure on the electron concentration. This observation is in accord with (71), (72), and experimental studies done by Jal (92), and Steininger (93).