Abstract
We have recently developed a general method for the calculation of electronic structures including many-electron interaction from first principles, which we call DV-ME method. In this paper, we report on its application to the calculations for multiplet structures of chromium ion pairs in ruby. The first and fourth nearest neighbour ion pairs were considered by the use of [CrCrAl2O16]20− model clusters. The results qualitatively reproduced not only the multiplet energies of the pair of ground-state chromium ions, but also those of the excited states arising from the spin-flip and charge-transfer transitions. The state with the minimum energy in the ground-state pair showed that the first nearest neighbour ion pair is antiferromagnetically coupled and the fourth nearest neighbour ion pair is ferromagnetically coupled. From the energy levels in the ground-state pairs, the exchange integrals J are also evaluated. The calculated signs of J are consistent with the results from experiments, indicating that the exchange integral J in the “classical” Heisenberg Hamiltonian can be calculated by first-principles calculation.
