Abstract The general formulas which are convenient for cluster analysis of a configuration interaction wave function are presented. These formulas are then used for cluster analysis of the “complete” configuration interaction wave functions of the π‐electronic models of benzene and butadiene obtained with a semiempirical method of the Pariser–Parr–Pople type using three different parameterizations. For butadiene the calculations are carried out with Hückel, Hartree–Fock, and Brueckner molecular orbitals. The results clearly indicate that Sinanoǧlu's statement [1, 2], concerning the relative unimportance of the linked parts of the tetraexcited state coefficients in the ci expansion, is justified for these delocalized systems.
A general contraction scheme for Gaussian basis sets is presented. The contraction coefficients are defined by the natural orbitals obtained from an atomic configuration-interac...
Methods of efficiently optimizing the orbitals of generalized valence bond (GVB) wavefunctions are discussed and applied to LiH, BH, H3, H2O, C6H6, and O2. The strong orthogonal...
We show than an ab initio molecular-dynamics scheme based on Vanderbilt ultrasoft pseudopotentials and a plane-wave expansion for the electronic orbitals allows one to perform a...
Abstract The coupled‐pair many‐electron theory, its linear approximation, and various other approximate coupled‐pair approaches based on the orthogonally spin‐adapted coupled‐pa...
The polarization configuration interaction (POL–CI) wavefunction is described. Calculations are reported for the X 3Σ−, a 1Δ, b 1Σ+, A 3Π, and c 1Π states of the NH molecules in...
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