Direct inversion in the iterative subspace (DIIS) optimization of openshell, excitedstate, and small multiconfiguration SCF wave functions
Abstract
The direct inversion in the iterative subspace (DIIS) method is applied to several simple SCF wave functions in an effective Fock matrix formulation. The following cases are treated: highspinrestricted open shell, openshell singlet, and twoconfiguration wave functions. Openshell singlet states are described by a threedeterminant 2×2 CAS expansion which is equivalent to Davidson's nonorthogonal SCF method in the case of the first openshell singlet. Very sharp convergence is usually obtained in less than 20 cycles. The method is applicable to slowly convergent or even inherently divergent cases, and able to enforce convergence to excited states not the lowest of their symmetry. For these simple wave functions, the present first order method is asymptotically more efficient than secondorder methods. Examples are presented for H_{2}O, H_{2}O_{2}, C_{2}H_{4}, F_{2}, several states of NO_{2}, C_{2}H_{5}, formaldehyde, and ketene.
 Publication:

Journal of Chemical Physics
 Pub Date:
 May 1986
 DOI:
 10.1063/1.449880
 Bibcode:
 1986JChPh..84.5728H
 Keywords:

 Inversions;
 Iterative Solution;
 Molecular Excitation;
 Self Consistent Fields;
 Wave Functions;
 Convergence;
 Formaldehyde;
 Ketenes;
 Nitrogen Dioxide;
 Optimization;
 Water;
 Atomic and Molecular Physics