Core effects in lithium hydride

Calculations of the directional Compton profiles and of the anisotropies of Compton scattering are reported, based on density-functional theory within the local-density approximation, performed using a plane-wave basis, and using (i) pseudopotentials and (ii) full, unscreened Coulomb potentials for both Li and H atoms. The pseudopotential calculations yield Compton profiles with unsatisfactory agreement with experiment. The reason of this failure is discussed. It is then shown that, with the total Coulomb potentials, converged results can be obtained, and that the Compton profiles obtained are in excellent agreement with experiment. Possibilities land limits) of extending the plane-wave calculations with the full Coulomb potentials to other atoms and substances are discussed. Furthermore, a simple method is proposed that allows the reproduction of the full Coulomb potential results at a much lower cost, by orthogonalizing the pseudo-wave-functions to the core orbitals calculated separately.