Molecular oscillations of ligand motions at the active site of carbonmonoxy myoglobin have been calculated in a protein environment using the combined QM/MM approach. In these calculations, the active site was calculated at a quantum mechanical (QM) level of theory using the B3LYP/6-31 + G* method, while the remaining protein was calculated at the molecular mechanical (MM) level utilizing the AMBER force field. The presence of a torsion mode and the second component of the bending vibration are proof of a bent CO geometry in the heme pocket. (c) 2005 Elsevier B.V. All rights reserved.