Evaluation of Thermal Expansion Coefficients Using Ab-initio Molecular Dynamics with Small Cell Sizes for Materials Design

The calculations of thermal expansion coefficients have been carried out using ab-initio molecular dynamics with a small cell containing only eight atoms that is a suitable calculation in size for materials design. Si, Ge, and GaP crystals were selected as the reference materials for comparison between calculation and experiment. The calculated lattice constants were in good agreement with experimental ones. The thermal expansion coefficients of three crystals were obtained from the temperature dependence of the lattice constants. There was reasonable agreement between the calculation and the experiment. Furthermore, even in use of the smaller cells containing two atoms for Ti, Cr, Fe, and four atoms for Al, Co, Ni crystals, the calculated thermal expansion coefficients were in good agreement with experiments. Our results proved firmly that there is a good possibility of obtaining the thermal expansion coefficients by ab-initio molecular dynamics even in use of a small cell for the calculations.