TOWARDS A CALCULATION OF THE ELECTRONIC-STRUCTURES OF MACROMOLECULES .1. QUADRATICALLY CONVERGENT METHOD FOR A DIRECT CALCULATION OF LOCALIZED MOLECULAR-ORBITALS

A super configuration-interaction method is applied to a direct calcul ation of orthogonal localized molecular orbitals (LMO). Its iterative procedure converges quadratically, retaining the initial forms of the LMOs. When the basis sets of large sizes are employed for the calculat ion, Davidson's diagonalization method can be adopted beneficially, wh ere the time-consuming four-index transformation of LMO integrals is r eplaced by simpler two-index transformations. Test calculations using double-zeta basis sets are reported in detail for H2CO (formaldehyde). B2H6 (diborane), C3H4 (1-propyne [metylacetylene]), and cytosine. Til e implication of the method concerning macromolecular calculations is discussed.