A Systematic First-Principles Study of Computational Parameters Affecting Self-diffusion Coefficients in FCC Ag, Cu, and Ni

Abstract

The diffusion coefficient of a metallic alloy system is critical to understanding phase transformations, mechanical properties, and failure mechanisms such as creep. Rather than performing costly and time consuming experiments, first-principles calculations based on density functional theory have emerged as a robust alternative to experimentally determined diffusion coefficients. In this work, first-principles calculations based on density functional theory are used to investigate the effects of varying the exchange-correlation functional and supercell size had on the accuracy of calculated self-diffusion coefficients. Self-diffusion and thermodynamic properties of Cu, Ni, and Ag are calculated using the two exchange-correlation functionals: the local density approximation and the generalized gradient approximation of Perdew, Burke, and Ernzerhof for solids. Supercells of 32, 64, and 108 atoms are used to investigate the minimum supercell size necessary to isolate the vacancy. Finally, two methods for accounting for vibrational entropy contributions due to temperature are employed: a simple estimation of the diffusion prefactor used previously in the literature and harmonic phonon calculations. The estimation of the diffusion prefactor produces acceptable results for Cu, but not for the other metals investigated. The harmonic phonon calculations improves both self-diffusion and thermodynamic properties when compared to experimental values for Cu, Ni, and Ag. For Cu and Ni, self-diffusion coefficients and related thermodynamic properties are consistent and stable regardless of the supercell size or exchange-correlation functional employed.