Convergence characteristics and effciency of mode-tracking calculations on pre-selected molecular vibrations

A detailed analysis of the recently introduced mode-tracking principle (J. Chem. Phys., 2003, 118, 1634) for the calculation of normal coordinates for pre-selected molecular vibrations is carried out. While previous studies have demonstrated the value of the method for tackling specific vibrational problems, a general feasibility study of the capabilities of the algorithm was missing and is presented here. The cyclohexanone molecule serves as a test system for the investigation of technical issues like numerical accuracy and convergence behaviour as well as for the study of spectroscopic issues like intermolecular vibrations and close-lying vibrational states which are subject to large couplings.