Localized electron pair theory for the calculation of ground state energies of large molecules

✍ Scribed by J.M. Cullen

• Publisher: John Wiley and Sons
• Year: 1992
• Tongue: English
• Weight: 743 KB
• Volume: 13
• Category: Article
• ISSN: 0192-8651
• DOI: 10.1002/jcc.540130715

✦ Synopsis

The quantum mechanical energy is examined in which groups of one, two, three, and four localized electron pairs found within a molecule are separately computed. From these results, the interaction energies of the electron pairs taken one, two, three, and four at a time form the terms of a convergent molecular mechanics like expansion of the molecular ground state energy. This procedure can be used with any size consistent quantum mechanical method. The computational time for large molecules depends chiefly upon the order needed in the energy expansion to obtain sufficient convergence and not on the particular quantum mechanical method used. Preliminary results within the framework of a semiempirical CNDOI2 model Hamiltonian show at the Hartree-Fock and M@ller-Plesset perturbation levels that relative energies converge to within a few tenths of a kcal/mol of the exact values at the four body level for molecules that have little delocalization. In strained ring and aromatic systems, convergence is however not nearly as rapid. Results can be improved somewhat by using larger interacting fragments containing two or more electron pairs over three or more atomic centers.