Hybrid method of studying LAM in clusters

A hybrid method for analyzing vibrations of molecules and complexes with potential energy surface (PES), that is characterized by a high level of anharmonicity, is proposed in present book. Distinctive feature of the method is the accounting of all vibrational degrees of freedom. Here the full set of vibrational coordinates is divided into two subsets. The first one contains coordinates for which PES of the limited dimensionality is the most anharmonic one. The second one contains coordinates for which PES of limited dimensionality is close to the harmonic one. Accounting of the intrinsic anharmonicity and anharmonic interaction of coordinates of the first subset is carried out by the construction of multidimensional PES, followed by numerical solution of the Schrödinger equation. Accounting of the intrinsic anharmonicity and anharmonic interaction of coordinates of the second subset, as well as anharmonic interaction between coordinates of different subsets, is carried out in frame of the standard model using second-order perturbation theory. Testing of the hybrid method was performed mainly on the molecular systems with hydrogen bonds.