  The Hartree-Fock based diagonalization is a computational method for the
investigation of the low-energy properties of correlated electrons in
disordered solids. The method is related to the quantum-chemical configuration
interaction approach. It consists in diagonalizing the Hamiltonian in a reduced
Hilbert space built of the low-energy states of the corresponding disordered
Hartree-Fock Hamiltonian. The properties of the method are discussed for the
example of the quantum Coulomb glass, a lattice model of electrons in a random
potential interacting via long-range Coulomb interaction. Particular attention
is paid to the accuracy of the results as a function of the dimension of the
reduced Hilbert space. It is argued that disorder actually helps the
approximation.
