Overestimation of melting temperatures calculated by first-principles molecular dynamics simulations

Area of Science:

• Computational materials science
• Condensed matter physics
• Physical chemistry

Background:

• Calculating melting temperature (Tm) using molecular dynamics (MD) simulations is challenging, with first-principles MD (FP-MD) often yielding significant overestimations.
• The accuracy of FP-MD for Tm is influenced by simulation parameters and material properties, necessitating careful assessment.

Purpose of the Study:

• To evaluate the accuracy of FP-MD simulations for calculating the melting temperature of various solids.
• To identify factors contributing to overestimations in Tm calculations, particularly for oxide materials.

Main Methods:

• Utilized first-principles molecular dynamics (FP-MD) simulations, emphasizing adiabatic conditions (no thermostat) to accurately capture liquid-state equilibria.
• Investigated the impact of cell size (approximately 100 atoms) and transition width (Wm) on Tm calculations for elements like Silicon (Si) and Sodium (Na).

Main Results:

• Adiabatic FP-MD simulations with ~100 atoms achieved good agreement for Tm of Si and Na, within the uncertainty introduced by the transition width (Wm).
• Demonstrated that surface contributions are unlikely to universally explain the need for solid-liquid coexistence methods in bulk solids.
• Observed consistent, large overestimations of Tm for oxide materials, irrespective of calculation conditions.

Conclusions:

• The overestimation of Tm in oxide materials is likely due to inherent errors in the Local Density Approximation/Generalized Gradient Approximation (LDA/GGA) electron correlation functionals.
• For elemental solids like Si and Na, FP-MD with appropriate cell sizes and adiabatic conditions can yield accurate Tm values.
• The findings provide insights into improving the reliability of MD simulations for predicting material melting points.