Electronic structures of polymers using the tight-binding approximation. III. Density matrix approach to poly-L-alanine and polyglycine-water complex by the CNDO/2 method

Abstract

In the present paper, formulas for calculating the electronic structure of polymers are derived in terms of the density matrix by the tight‐binding approximation using the CNDO/2 method. This formalism was successfully applied to poly‐L‐alanine, which was difficult to treat by the usual SCF procedure because of the divergent behavior of the iterative calculation. The obtained result indicates that the right‐handed α‐helical conformation is more stable than the left‐handed one and the planar one in agreement with experiments. The analysis of the total energy leads to the finding that the interaction between the methyl group and the carbonyl group is responsible for determining the relative stability of two α helices. Finally, the effect of water hydrogen‐bonded to polyglycine was studied from the view point of the polymer effect.