J. Delhalle, J. G. Fripiat, 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

(Submitted to Int. J. Quantum Chem., August, 2001)

The purpose of this paper is to point out to the scientific community interested in Hartree-Fock ab initio calculations that accurate calculations of the exchange contributions are essential. An extremely simple system such as the infinite chain of Be atoms (-Be-)_infinity treated in direct space at the RHF level with the 3-21G basis fails to converge to physically meaningful results. An analysis based on the convergence properties of finite Fourier series points to the exchange contributions as the source of the problem. Owing to its capability of handling with the necessary accuracy all lattice summations, including the exchange sums, the Fourier representation is able to treat the problem effectively and is confirmed as a procedure of choice for RHF electronic structure calculations of systems with 1D periodicity.