AB-INITIO ELECTRONIC-STRUCTURE CALCULATION OF A NEW GENE SYSTEM USINGTHE NEGATIVE FACTOR COUNTING METHOD

We report a calculation of the electronic structure (density of states and molecular orbitals) of a new gene system-the plasmid shuttle vect or pCRR1-performed at the ab initio Hartree-Fock level. To deal with t he aperiodicity of the biopolymer, a vectorized version of a negative factor counting (NFC) program has been implemented. With this efficien t tool, DNA molecules of up to 100 deoxynucleotides (similar to 10,000 basis functions at the ab initio level) can be calculated routinely. In our calculation the base sequence of the plasmid is explicitly take n into account and a standard helical structure is assumed. Minimum as well as 6-31G basis sets are used in the calculation, and solvation e ffects are explicitly included. The calculation shows that solvation d oes not have a significant effect on the electronic structure of the b iopolymer. It is found that the frontier orbitals (HOMO and LUMO) are highly localized on the bases. The interpretation of this result in te rms of the frontier molecular orbital theory is that the attack of rad iation-induced radicals is mainly on the base moieties. (C) 1998 by Ra diation Research Society.