A quantum chemical method is proposed for the conformational analysis of very large biomolecules. The total wave function is constructed of localized bond fragments each determined on the basis of chemical intuition and model calculations on small molecules. The transferability of bond orbitals, localized strictly onto a few atoms of the molecule is discussed. The Löwdin procedure is applied to obtain orthogonalized molecular orbitals. The energy expression is calculated using the ZDO assumption. Simplified formulas for the Coulombic-type electronic interaction integrals are introduced. This approximation is similar to the assumption of the CNDO-method made in order to maintain rotational invariance. To obtain an energy expression, containing a number of terms proportional to N2, (N is the number of occupied orbitals) the overlap of non-adjacent bond orbitals is neglected. At last a simple point-charge interaction is assumed to act between atoms lying far from each other. Thus the calculation of the energy involves the evaluation of a number of integrals proportional to the first power of N. Numerical results for H2, Li2 and LiH are given.
ASJC Scopus subject areas
- Nuclear and High Energy Physics