BOX ORBITALS FOR EXTENDED SYSTEMS

A linear scaling of the number of nonzero integrals in extended system s calculations and the solution of the difficult cutoff threshold prob lems in the integral evaluation of periodic HF computations could be s olved by the usage of orbitals with a finite extension. The present wo rk proposes the usage of Box orbitals, defined inside spheres centered on the nuclei. Preliminary tests on small systems (atoms and H-2(+)) were performed. The results ale very encouraging, since, in most cases , the Box orbitals give better results (giving results of equivalent q uality in the worse cases) than do the classical Gaussian orbitals. No spurious effects were encountered. (C) 1997 John Wiley & Sons, Inc.