Analysis of the Thouless coherent state using the 1/K expansion.

Abstract

The many-electron problem in a spin-orbital basis of rank K, with a Hamiltonian exhibiting the unitary group U(K) (the coherence group), global symmetry is treated as a detailed example of the technique often referred to as the 1/K expansion. This approach introduces a free parameter K, which is a measure of the number of dynamical variables and usually also invokes coherent states associated with the coherence group. We choose the Thouless coherent state, transform the complex state parameters so that they exhibit the structure of a flat generalized phase space, and analyze the corresponding energy functional as a power series in 1/K. The limit of large K and that of a large number of electrons are discussed and compared to the expected classical limit.