Temperature dependent electronic structures and the negative thermal expansion of \delta -Pu

TL;DR

This study introduces a temperature-dependent parameterization in a classical force field to accurately simulate the thermal expansion and phonon behavior of delta-phase plutonium, highlighting the importance of temperature effects in modeling complex materials.

Contribution

The paper develops a novel temperature-dependent parameterization for the embedded-atom method, improving the simulation of plutonium's thermal properties over previous temperature-independent models.

Findings

Captures negative thermal expansion in delta-Pu

Shows phonon softening near zone boundary with temperature

Highlights importance of temperature-dependent modeling

Abstract

We introduce a temperature-dependent parameterization in the modified embedded-atom method and combine it with molecular dynamics to simulate the diverse physical properties of the \delta - and \epsilon - phases of elemental plutonium. The aim of this temperature-dependent parameterization is to mimic the different magnitudes of correlation strength of the Pu 5f electrons at different temperatures. Compared to previous temperature independent parameterization, our approach captures the negative thermal expansion and temperature dependence of the bulk moduli in the \delta -phase. We trace this improvement to a strong softening of phonons near the zone boundary and an increase of the f-like partial density and anharmonic effects induced by the temperature-dependent parameterization upon increasing temperature. Our study suggests it is important to include temperature-dependent parameterization in classical force field methods to simulate complex materials such as Pu.