Transition phenomenon in Ti2O3 using the discrete variational Xa cluster method and periodic shell model

The electronic structure of the metallic Ti2O3 and insulating phases has been investigated using a combination of the three-dimensional periodic shell model and the discrete-variational (DV)-Xa cluster method. Besides the effects of intersite repulsive nearest-neighbor electron-electron (d-d) Coulombic interaction and the spin-spin interaction by means of a generalized Hubbard Hamiltonian, the Hamiltonian in the insulating phase includes Anderson’s attractive potential due to the electron-phonon interaction. The shell model estimates the electron-phonon coupling constants, and provides direct theoretical evidence that the electronphonon interaction stabilizes the three dimensional periodic distribution of Ti2Ti pairs along the c axis of the corundum structure. The DV-Xa cluster method calculates the electron energies in the @Ti2O9# 212 cluster, the values for the intersite repulsive nearest-neighbor d-d interaction, and the spin-spin interaction. The electron correlation effect and the spin correlation effect are found to be mainly responsible for the broad crossover between a metallic and an insulating state in Ti2O3, although there is some contribution from the electron-phonon interaction. The present calculation describes the characteristic transition phenomenon in this material. @S0163-1829~97!07744-8#