The comparison of the self-consistent pseudopotential and orthogonalised plane wave charge densities for trigonal Se

The charge densities calculated with the self-consistent symmetrised orthogonalised plane wave (SCSOPW) method (Xa: alpha =1235 SOPW at each of the symmetry points Lambda , A, K, H, K', H', L and M) for trigonal Se are compared triplet by triplet with the self-consistent pseudopotential (SCPSP) densities of Starkloff and Joannopoulos (1978). The SCSOPW charge density maxima are typically twice as high as the SCPSP maxima. The SCSOPW charge density of the lowest triplet shows clear intrachain pile-ups which are missing from the SCPSP density. The reasons for the differences are discussed.