Tests of the Harris energy functional

Tests of the Harris energy functional are presented for a number of different systems, using the pseudopotential total energy method within local density theory. Using an input charge density consisting of a superposition of pseudo-atomic charge densities the authors evaluate the Harris and Kohn-Sham energy functionals and compare with the self-consistent results. They calculate the lattice constant, bulk modulus and some phonon frequencies of silicon and the aluminium (111) surface energy. For the bulk properties of silicon both functionals yield good agreement with the self-consistent results without the need for self-consistency. For the aluminium surface energy neither functional agrees well with the self-consistent solution. However, for a range of input charge densities the Harris functional consistently gives better results than the Kohn-Sham functional. This result is explained in terms of the long-wavelength instability encountered in solving the Kohn-Sham equations.