Cancellation of low order electric moments of the unit cell: An efficient way of calculating crystal field effects in Hartree-Fock computations on periodic systems

In the framework of a real quantum mechanical problem, we investigate the modified unit cell concept in order to calculate the crystal field effects in periodic systems. We make use of a recently proposed procedure based on the cancellation of the unit cell low order electric moments. Applied to a one-dimensional periodic chain of lithium hydride molecules, this procedure compares in an excellent way with the recently developed multipole expansion technique and offers a dramatic improvement of the results with respect to the usual cluster-type approaches.