On the prospective use of the one-electron density matrix as a test of the quality of Post-Hartree-Fock schemes for crystals

It is argued that experimental determinations of the one-electron density matrix of crystalline systems, gamma(1) (r, r'), based on directional Compton profiles and X-ray structure factors could be useful to assess the quality of computational techniques which take electron correlation effects into account. A scheme is here outlined for evaluating the correlation correction to the Hartree-Fock one-electron density, starting from the solution obtained for the periodic system at a perturbative MPn level. The case of crystalline lithium hydride is discussed. Preliminary MP2 results for that system are presented, obtained using a local-correlation approach.