Embedded cluster calculations of metal complex impurity defects: properties of the iron cyanide in NaCl

We present the results of calculations of the {[FeCl6-n(CN)(n)](m-) x (V-Na )(5-m)} (5-)impurity complex incorporated in the NaCl crystal lattice. A nu mber of characteristic defect configurations are calculated quantum mechani cally using an embedded cluster method, and compared with the results of Mo tt-Littleton (ML) calculations. We investigate the electron affinity and th e orientation of CN- ligands. The dependence of vibrational frequencies of the CN stretching mode on the ligand orientation, charge of the impurity an d the relative position of the ligands and the charge compensating vacancie s are calculated. Analysis of these results demonstrates the ability of ML calculations to predict the relative stability of different configurations of this particular family of defects. Comparison of the ML and embedded clu ster calculations reveals the contributions to the defect energy and stabil ity.