Correlation corrected band structures of different homopolypeptides Part II. Quasi-particle band structures of seven homopolypeptides with aliphatic side chains

Abstract

The Hartree–Fock (HF) crystal orbital method for polymers with an arbitrary number of basis functions per unit cell has been is outlined. Starting from the HF energy bands and crystal orbitals it is briefly shown, how one can correct the energy band structure for correlation using the inverse Dyson equation in its diagonal approximation. For the self energy occurring in the Green’s matrix formalism the computationally simple Moeller–Plesset 2 (many body perturbation theory in second order) expression has been used. For seven homopolypeptides, poly(Gly), poly(Ala), poly(Ser), poly(Thre), poly(Leu), poly(iLeu) and poly(Val) the correlation corrected band structure calculations were performed. The results obtained are compared to the previous LDA calculations for the same systems. In agreement with general experience the fundamental gap values are much larger than the too small LDA values. The correlation corrections decrease the gap by 2–3 eV, but they are still larger by ∼3 eV than the values which can be estimated on the basis of intermediate exciton theory.