Thermal expansion and mode Grüneisen parameters of LiH and LiD

The third order contribution of the shell-shell interaction between next nearest neighbours has been determined from a calculation of the coefficient of linear thermal expansion of LiH and ⁷LiD. The Coulomb anharmonicity is included. A shell model fitted to phonon energies from inelastic neutron scattering in ⁷LiD was used. From this model then averaged Grüneisen constants and individual mode Grüneisen parameters have been deduced.