A density functional study of copper hydroxonitrate: size effects and spindensity topology

Copper hydroxonitrate has been investigated within density functional theor y and a plane-wave approach. In order to elucidate the topology of the spin density distribution and the microscopic origins of the antiferromagnetic character of this compound, systems with an equal number of unit cells diff erently oriented in space have been considered. Parallel and antiparallel a lignment of spin densities occur between Cu centers, the coupling pattern v arying from one plane to the other. Depending on their coordination with th e Cu atoms, O atoms carry non-negligible spin densities. These are larger f or oxygens on hydroxo groups bridging those Cu atoms which have spin densit ies aligned in a parallel fashion. The spatial distribution of spin densiti es is far from being unique, suggesting that the S=0 global spin state is c ompatible with different local spin structures very close in energy. (C) 20 01 Elsevier Science Ltd. All rights reserved.