Phonon Energies and Lifetimes in Solid Ne and He in the First-Order Self-Consistent Approximation

We discuss the response of a crystal in the presence of a neutron distortion in the first-order self-consistent approximation and we stress the importance of the self-consistency condition. The resultant integral equation for the phonon energies is solved by direct matrix inversion instead of truncating a series expansion. Numerical results are presented for solid Ne and fcc He⁴ at 10.0 and 11.5 cm³/mole.