Application of the DIIS technique to improve the convergence properties ofthe SCF-MI algorithm

The direct inversion in the iterative subspace (DHS) technique of Pulay is incorporated within the self consistent field for molecular interactions (S CF-MI) algorithm. It is shown to improve significantly the convergence rate of the conventional SCF-MI iteration scheme. The implemented procedure dem onstrates stability and rate of convergence similar to that of standard DII S-based codes. Its performance is compared to that of the level-shifting te chnique as applied within the SCF-MI algorithm on test examples involving m olecular complexes and standard basis sets. (C) 2001 Elsevier Science B.V. All rights reserved.