Density functional embedding approach to the Mn impurities in NaBr crystals

Abstract

We have performed density functional calculations for three 19-atom clusters, two 25-atom clusters, and one 18-atom cluster, each embedded in a Madelung potential that takes into account the long-range electrostatic interactions of the ion lattice of a NaBr crystal. One of the three 19-atom and one of the two 25-atom clusters model bulk crystalline NaBr

the others model a Mn2+ impurity trapped in a cubically symmetric crystalline electric field (CEF) site of the NaBr host. One of the latter has the NaBr bulk interatomic distance, while in the others relaxation of the Br atoms around the metallic impurity has been considered. The 18-atom cluster models a relaxed Mn impurity Na vacancy system. All of our calculated clusters have a Na site at the center, and they all include at least first and second nearest-neighbor host atoms. In the center of the doped clusters the Mn impurity replaces the missing Na ion. The electronic structure of the embedded impurity ion in its local environment was computed self-consistently by means of ah-electron density functional theory (DFT) techniques. We have examined the lattice relaxation around the impurity and calculated the hyperfine coupling constants (HFCC). The results for the Mn electronic structure and for the HFCC are in agreement with experimental results using electron paramagnetic resonance measurements. (C) 2000 John Wiley & Sons, Inc.