ON THE SCATTERED-WAVE X-ALPHA CALCULATION OF POTENTIAL-ENERGY SURFACES FOR TRANSITION-METAL IMPURITIES IN IONIC LATTICES - MN2+ AND CU+ IN NAF

Cu+ and Mn2+ impurities in NaF are studied within the perturbed cluster approximation. The MTX-alpha-method is used to compute potential energy curves for the a1g vibrational modes of CuF6(5-) and MnF6(4-) clusters embedded in the host. The clusters are stabilized by an electrostatic lattice potential evaluated analytically from Slater orbital (SO) approximations to the true lattice ion wave functions. This approach is superior to the common Watson sphere model for the cluster environment, but gives unsatisfactory muffin-tin total energy curves. To remedy this, the implementation and evaluation of non-muffin-tin corrected total energies for embedded clusters is described and shown to give improved results. Further refinements to the model are discussed.