Heisenberg-Dirac-van Vleck model applied to describing the magnetic parameters of mixed-valency clusters

A study has been made on using a Heisenberg-Dirac-van Vleck model in the magnetochemistry of class II mixed-valency cluster compounds. That model may be modified with allowance for electron transfer but cannot be applied to mixed-valency dimers when there is a high degree of excess-electron localization but with small values of the exchange integral. For large values of the exchange integral, that model leads to an incorrect value for the ground-state spin even for localized systems. The correct approach here is based on calculating the spin-vibronic energy spectrum.Translated from Teoreticheskaya i Éxperimental'naya Khimiya, Vol. 28, No. 2, pp. 121–124, March–April, 1992.