Development of hybrid method using ab initio and classical molecular dynamics for calculating the thermal expansion coefficient of alloys at high temperature

In order to predict the thermal expansion coefficient (TEC), quasiharmonic approximation based on the ab initio electronic structure calculation is an effective and conventional scheme. However, it is known that the deviation due to anharmonic effect arises at high temperature. Although Molecular Dynamics (MD) naturally includes the anharmonic effect, classical MD is lacking in accuracy because of its empirical interatomic potential and ab initio MD is not applicable because of its high computational cost. In this paper, we have proposed a new hybrid method using ab initio electronic structure calculation and classical molecular dynamics for calculating TEC of alloys at high temperature. Our method is non-empirical, highly accurate and computationally inexpensive. The method consists of three steps. Firstly, various snapshots of the atomic coordination at a certain temperature are sampled by classical MD. Secondly, physical properties of each snapshot are calculated by ab initio electronic structure calculation. Finally, by analyzing them statistically, the equilibrium volume is computed. TEC is obtained by repeating these steps at different temperatures. We have calculated the TECs of Al, Ni3Al, and NiAl. Results show good agreements with experimental results. Our method enables us to improve the conventional quasiharmonic approximation and obtain accurate TEC at high temperature through the incorporation of anharmonic effect. © 2018 The Society of Materials Science, Japan.