Diffusivities of Cu-Ni and Cu-Si liquids calculated via ab initio molecular dynamics and the assessment of atomic mobilities

Abstract

In the literature, information pertaining to self- and impurity diffusivities of liquid phases for metals, non-metals, etc. is very scarce. The reason for scarcities is difficulty in performing experiments. The difficulties will be aggravated for pure elements or alloys with high melting points. The advent of efficient computing resources could serve to overcome this experimental snag. Here we report a hybrid methodology of AIMD and CALPHAD approach to obtain an atomic mobility parameter for liquid Cu-Ni and Cu-Si systems in wide composition and temperature ranges. As a part of this hybrid approach, the calculation of self- and impurity diffusion coefficients for Cu-Ni and Cu-Si liquids via ab initio molecular dynamics (AIMD) technique in conjunction with Einstein's diffusion equation is performed. The experimental densities (ρ) for Cu-Ni and Cu-Si are used to fix the volume (V) of the super-cell for AIMD simulations. There are total of 64 AIMD simulations in this work. For each binary system, the simulations are performed for eight compositions at four different temperatures. The simulated results at different temperatures are used to extract the activation energies and the frequency factors for different compositions. The CALPHAD-type atomic mobility assessments for the liquid phases of Cu-Ni and Cu-Si are based on the AIMD diffusivities calculations from this work. The comparisons of the CALPHAD calculations, experimental measurements, and the AIMD simulations are also given. We believe that this hybrid methodology- AIMD results for CALPHAD-type mobility assessments, will be an interesting addition to the existing literature. It is also highly expected that the presently developed methodology to assess the atomic mobilities is equally valid for other systems.