A correlated ab initio study of Karplus relations for model peptides

The equation-of-motion coupled cluster (EOM-CCSD) method was employed to st udy the variation of proton-proton NMR spin-spin coupling constants with th e dihedral angle for coupled protons while all other bond lengths and angle s were allowed to relax. N-Methylacetamide was chosen as a frequently studi ed prototype of substantial experimental interest. The constants (A, B and C) governing the behavior of the coupling constants with the dihedral angle were determined in a fully ab initio, correlated manner and were compared with others in the literature. Copyright (C) 2001 John Wiley & Sons, Ltd.