5 Hartree–Fock approximation
In the last chapter, we showed that the Hamiltonian for interacting electrons in a solid can be written in second-quantized form as
where and the Greek letters denote single-particle orbitals. In this chapter, we introduce the Hartree–Fock approximation to the correlated electron problem. The basic assumption of this approximation is that the ground state is the same as that of the non-interacting system. The energy is taken to be the expectation value in this state.
5.1 Non-interacting limit
Let us ...