New Methods for Calculating the Free Energy of Charged Defects in Solid Electrolytes

TL;DR

This paper introduces a Monte Carlo-based method to accurately compute the free energy of charged defects in solid electrolytes, extending beyond ideal solution approximations and reducing computational effort.

Contribution

It presents a novel approach combining Wang-Landau Monte Carlo with electrostatic calculations to evaluate defect free energies efficiently.

Findings

Accurately describes free energy up to 10% defect concentration

Extends beyond ideal solution theory

Reduces the number of temperature-dependent simulations

Abstract

A methodology for calculating the contribution of charged defects to the configurational free energy of an ionic crystal is introduced. The temperature-independent Wang-Landau Monte Carlo technique is applied to a simple model of a solid electrolyte, consisting of charged positive and negative defects on a lattice. The electrostatic energy is computed on lattices with periodic boundary conditions, and used to calculate the density of states and statistical-thermodynamic potentials of this system. The free energy as a function of defect concentration and temperature is accurately described by a regular solution model up to concentrations of 10% of defects, well beyond the range described by the ideal solution theory. The approach, supplemented by short-ranged terms in the energy, is proposed as an alternative to free-energy methods that require a number of simulations to be carried out over a range of temperatures.