  Hydrogen single-particle dynamics in solid LiH at T=20 K has been studied
through the incoherent inelastic neutron scattering technique. A careful
analysis of the scattering data has allowed for the determination of a reliable
hydrogen-projected density of phonon states and, from this, of three relevant
physical quantities: mean squared displacement, mean kinetic energy, and
Einstein frequency. In order to interpret these experimental findings, a
fully-quantum microscopic calculation has been carried out using the
variational Monte Carlo method. The agreement achieved between neutron
scattering data and Monte Carlo estimates is good. In addition, a purely
harmonic calculation has been also performed via the same Monte Carlo code, but
anharmonic effects in H dynamics were not found relevant. The possible
limitations of the present semi-empirical potentials are finally discussed.
