Validation of semiempirical methods for modeling of corrinoid systems

Several semiempirical methods (MNDO-d, PM3tm, PM3-d, PM5, PM6, and AM1-d) have been tested against experimental data and density functional theory (DFT) results in search for the best methods that can be used for quantum-mechanical-molecular mechanics (QM/MM) modeling of corrinoid systems of vitamin B(12) co-factor. It has been found that the PM6 parametrization in its present form gives results closest to hybrid DFT calculations that are most widely used thus far. In comparison with pure DFT and experimental data the best agreement is obtained for PM3tm parametrization, while PM6 yields slightly worse results. AM1-d yields bad geometry of the corrin moiety. The worst performance was observed for MNDO-d, which has severe problem with position and orientation of the alpha-ligands.