Total energies of structural defects in glassy Se

Abstract

The effective Hubbard U is calculated for the interconversion of 1-fold and 3-fold bonding coordination defects in glassy Se. This is accomplished by applying local density total energy calculations directly to charged defects in a superlattice configuration. It is found that the defect remains 1-fold coordinated in the D − and D 0 charge states, but spontaneously forms a 3-fold center in the D + charge state. The structural relaxation energy involved in the bond switching gives rise to a sizable negative contribution to U, but a still larger Coulomb repulsion gives rise to an overall positive U. This result is not, however, inconsistent with a negative U in the compound chalcogenide glasses.