A First-Principles Investigation of the Diffusion Properties of Paired Gold Solute Atoms in a Silver Lattice using the 14-frequency Model

Diffusion is of great interest to the materials science and engineering community and directly affects phase transformations, mechanical properties, and failure mechanisms of a material. Experimentally determining the diffusion coefficients can be an expensive and time consuming process. Using computational techniques based on density functional theory (DFT) to predict the diffusion coefficients within alloy systems is an extremely useful alternative. Calculating diffusion related properties of metal systems using first-principles techniques for self-diffusion and in the presence of one impurity atom are well established techniques. The next step in diffusion modeling using first-principles methodologies is to calculate diffusion properties in alloy systems with paired solute atoms. In the present work, DFT-based calculations are carried out in an FCC silver host lattice with two gold impurity atoms present. The present work uses Bocquet’s proposed 14-frequency model to calculate all of the possible jump frequencies of lone and paired gold solute atoms in silver host matrix. The diffusion properties for self-diffusion of silver and the 5-frequency model calculations for a single gold solute in a silver host matrix are validated with well-known experimental data. The 14-frequency model allows for calculation of the solvent and solute enhancement factors, as well as for comparisons between jump frequencies relative to their host/solute atom placement.

The atomic jump frequencies are calculated using VASP within the generalized gradient approximation as implemented for solids by Perdew, Burke and Ernzerhof using a 108-atom supercell. The nudged elastic band method is used to calculate the minimum energy pathways of the diffusing atom. Thermodynamic properties at finite temperatures are calculated using the quasi-harmonic Debye model. A code written as part of the present work is implemented for the quasi-harmonic Debye model using the Birch-Murgnahan equation of state fitting curve as inputs.