I. Flamant, J. G. Fripiat, J. Delhalle, and Frank E. Harris

Facultes Universitaires Notre-Dame de la Paix, Namur (Belgium)

Department of Physics, University of Utah

Quantum Theory Project, University of Florida

Theoret. Chem. Accounts **104**, 350-357 (2000)

Formulas are presented for restricted Hatree-Fock (RHF) calculations on systems with periodicity in one dimension using a basis set of contracted spherical Gaussians. Applying Fourier-space and Ewald-type methods, all lattice sums appearing in the formulation have been brought to forms exhibiting accelerated convergence. Calculations have been carried out for infinite chains of Li_2 molecules and a poly(oxymethylene) chain . The methods used here yield results that are far more precise than the corresponding direct-space calculations and for the first time show the vanishing of the RHF density of states at the Fermi level for situations of partial band occupancy. Our initial computational implementation was about 5 times slower than the fastest direct-space code, but improvements in special-function evaluations and numerical integrations over the Brillouin zone are shown to remove this disparity in computing speed.