Utilization of ‘pseudo-lattice symmetry’ in cluster calculations

Cluster calculations which model chemisorption on a surface are often composed of substrate atoms arranged in a periodic manner. This pseudo-lattice symmetry of a cluster is used to reduce the number of 2-electron integrals computed in a SCF calculation by evaluating only unique integrals identified by lattice displacement vectors. The method, without using any explicit symmetry, is shown to be competitive with calculations which utilize point group symmetry. It is also demonstrated that the pseudo-lattice method markedly reduces the number of 2-electron integrals in multi-layer clusters which have little or no symmetry.