A wave-function approach to solids

Hartree-Fock (HF) method is a useful first-step tool for investigating electronic structure and total energy of atoms and molecules: it gives very good electron density, reasonably accurate total energy, and molecular orbitals and orbital energies that are helpful for understanding the electronic structure. The HF method is, however, not commonly applied to solids nowadays, since electronic screening effect is neglected, thereby resulting in vanishing density of states at the Fermi level of metals and serious overestimation of band gap of semiconductors. Although systematic improvement is considered to be an advantage of wave function theory (WFT) against the density functional theory (DFT), so-called post-HF methods are computationally too demanding for solids. For long, therefore, variational Monte Carlo (VMC) method and diffusion Monte Carlo (DMC) method have been only practical ways to calculate accurate total energy of solids within WFT.