ON THE MAGNETIC COUPLING IN NIO

The results are reported of nb initio calculations on the magnetic ord ering in NiO, a prototype of the antiferromagnetic insulator. By analy zing wave functions for different cluster models, information is obtai ned about the physical effects determining the sign and the magnitude of the magnetic coupling parameter J. The role of the edge oxygens, su rrounding the essential unit (Ni2O), is found to be quantitatively imp ortant but purely environmental in contrast to the role of the bridgin g oxygen. Furthermore, the importance of electron correlation and the usefulness of pseudopotentials in the calculations is investigated. Th e final result for J compares reasonably with experiment (about 50%), and possible sources for the remaining discrepancies are discussed. (C ) 1997 American Institute of Physics.