Ab initio MO approach to the magnetic interactions in chain structure of A2MnF5

We studied the magnetic interactions in the chain structures of A 2 Mn III F 5 by an ab initio MO method using cluster model molecules. The effective exchange integral (J) in the chain structures has been estimated from the total energy difference between the highest and lowest spin states in the alternant MO method. We calculated also a dependence of angle (Mn-F-Mn) of the J value in the cluster model. The calculated values are in agreement with the experimental ones. We also discuss a change of the overlap integral between d orbital of Mn and p orbital of F atom to confirm the dependence of angle for the exchange interaction.