ABSTRACT
When Hartree–Fock theory was first under development, Hartree–Fock approximations to many-electron wave functions often were assumed to be single Slater determinants. As explained in chapter 1, such wave functions, in general, are not eigenfunctions of the total angular momentum operators. In current atomic physics it is customary to define the Hartree–Fock approximation as a stationary solution of the variational problem (1.60) for a single configuration state function and the Hartree–Fock energy, the stationary energy associated with this solution. A special case is the fixed- or frozen-core Hartree–Fock (FCHF) approximation where orbitals defining the core are not allowed to vary.
