PHASE-TRANSITIONS FOR N-ELECTRON ATOMS AT THE LARGE-DIMENSION LIMIT

Symmetry breaking of electronic structure configurations for N-electro n atoms in weak magnetic and electric fields at the large-dimension li mit is described in terms of standard phase transitions. This symmetry breaking, which leads to ionization, is completely analogous to phase transitions and critical phenomena in statistical mechanics. This ana logy is shown by allowing the nuclear charge to play a role analogous to temperature in statistical mechanics. For the exact solution of N-e lectron atoms at the large-dimension limit, the symmetry breaking is s hown to be a first-order phase transition. For the special case of two -electron atoms, the first-order transition shows a triple point where three phases with different symmetry coexist. Treatment of the Hartre e-Fock solution reveals a different kind of symmetry breaking where se cond-order phase transitions exist for N=2. We show that Hartree-Fock two-electron atoms in a weak external electric field exhibit a critica l point with mean field critical exponents (beta = 1/2, alpha = 0(dis) , delta = 3, and gamma = 1).