DENSITY-FUNCTIONAL THEORY FOR JAHN-TELLER SYSTEMS

The first discussion of the dynamics of Jahn-Teller systems in terms o f the electronic density as the fundamental variable was given by W.J. Clinton in 1960, where the degenerate electronic configuration of a J ahn-Teller molecule was interpreted in terms of the infinite number of ways in which the charge distribution can be oriented for the same en ergy. The moving nuclear framework serves as the perturbation necessar y to define the orientation of the charge density, with no activation energy required to put the charge cloud into motion. Recently, this no tion of the electronic charge cloud in a Jahn-Teller molecule sweeping out the potential surface over which the nuclei move has found mathem atical expression in our work in terms of a generalized electronic cur rent density in nuclear-coordinate space [N. Sukumar and B.M. Deb, Int . J. Quantum Chem. 40, 501 (1991)]. The introduction of the electronic phase as a function of both electronic and nuclear coordinates, in ad dition to the electronic density, is a crucial component of this formu lation. In the present work, the density-based treatment is extended t o the nonadiabatic situation, with the Born couplings interpreted as n onadiabatic currents in parameter space. Abelian and non-Abelian gauge transformations of these currents are discussed. (C) 1994 John Wiley & Sons, Inc.