Passing the one-quadrillion limit in FCl extrapolations on a personal computer

An efficient algorithm for the full configuration interaction (FCI) on a personal computer is presented. Selected configuration interaction and second-order perturbation theory (PT) are combined to approach the full-CI limit. Comparison was made to existing full-CI benchmarks. A test calculation of NH2 symmetrical dissociation shows that the running time for finding the correlation energy with an accuracy of 0.1 kcal/mol is just 5 min on an IBM 486DX2-66 PC. As another example, the approximate full-CI calculations of the HF dimer in the (4s3 1d/2s 1p) and the (43 3p 1d/2s 1p) basis sets have been carried out. The ground state of (HF)2 produces 3 × 1014 and 4 × 1015 determinants, respectively.