Sesame-Style Decomposition of KS-DFT Molecular Dynamics for Direct Interrogation of Nuclear Models

TL;DR

This paper introduces an algorithm to extract nuclear and electronic thermal contributions from quantum molecular dynamics, applying it to liquid aluminum to compare with existing semi-empirical models, advancing understanding of high-temperature nuclear behavior.

Contribution

The paper presents a novel algorithm for decomposing QMD data into nuclear and electronic thermal contributions, enabling detailed analysis of nuclear behavior above melting temperatures.

Findings

The algorithm successfully extracts nuclear and electronic contributions from QMD simulations.

Comparison shows deviations of semi-empirical models from QMD results at high temperatures.

Results improve understanding of nuclear thermodynamics in liquids at extreme conditions.

Abstract

A common paradigm used in the construction of equations of state is to decompose the thermodynamics into a superposition of three terms: a static-lattice cold curve, a contribution from the thermal motion of the nuclei, and a contribution from the thermal excitation of the electrons. While statistical mechanical models for crystals provide tractable framework for the nuclear contribution in the solid phase, much less is understood about the nuclear contribution above the melt temperature ($C_v^{(\text{nuc})}\approx 3R$) and how it should transition to the high-temperature limit ($C_v^{(\text{nuc})} \sim \frac{3}{2}R$). In this work, we describe an algorithm for extracting both the thermal nuclear and thermal electronic contributions from quantum molecular dynamics (QMD). We then use the VASP QMD package to probe thermal nuclear behavior of liquid aluminum at normal density to compare the results to semi-empirical models -- the Johnson generic model, the Chisolm high-temperature liquid model, and the CRIS model.