First‐Principles Thermal Expansion in Rb and Cs

The thermal expansion of Rb and Cs is investigated using Toya's first‐principle approach with modified g ‐function. The mode Grüneisen parameters γ qj and the temperature dependence of both, the mean Grüneisen parameter γ T and the thermal expansion coefficient β T are calculated and compared with the experimental data available up to the present time. The agreement obtained between theory and experiment is satisfactory.