Applications of a novel algorithm for the calculation of MCSCF wavefunction: a look into possible avenues of convergence acceleration

Abstract

The efficacy of a method based on the direct inversion in the iterative subspace (DIIS) in accelerating the approach to self consistency in the calculation of the MCSCF wavefunction using a novel algorithm developed earlier, is compared with that of a simple damping technique. Although the 'damping' turns out to be ineffective in the 'quadratic region', it accelerates remarkably in the rate of descent on the energy hypersurface in the early stages of the iterative process which leads to an impressive overall increase in the rate of approach to self consistency. TheDIIS based procedure turns out to be ineffective when coupled to the present method and is plagued by ill conditioning problems. Calculations are done to compute the equilibrium geometrical parameter, charge density on different atoms, and dipole moment of HNO molecule in the lowest^1,3 nπ^∗ states at theINDO/2-MCSCF level.