Аннотация:A method for the analysis of internal dynamics of nonlinear weakly bound polymolecular systems based onthe effective-mode approach is proposed. The method enables one to estimate the number of the governingcollective degrees of freedom of the system of interest at a preset accuracy under particular conditions andanalyze the character of the modes depending on the activation energy of the system and the duration of itsdynamic propagation, which provides qualitative and quantitative information about the coupling of diversemotions and the respective energy redistribution. The method is applied to the analysis of the dynamics ofsmall water clusters stabilized by hydrogen bonds, which are unique spectacular examples of the systems with apronounced coupling between the intramolecular and substantially delocalized intermolecular oscillations. Thedynamic trajectories were generated in the adiabatic approximation at the Born-Oppenheimer level with theuse of the quantum chemical description of selected clusters at the MP2/6−311++G(d, p) level. The initialconditions corresponded to different variants of the excitation of low-frequency normal modes, and the dynamicruns were carried out at a time step of 0.5 fs and the whole duration of 50 to 100 ps. Different prevailing charactersof the cluster dynamics were identified depending on the molecular size, the total activation energy, and themean potential-energy-increment to kinetic-energy-increment ratio, from an efficient accumulation of the excesskinetic energy on the effective modes of the cluster to the dissociation of the cluster into constituting fragments.The signs of the corresponding processes in the overlap matrices of the effective-mode vectors, kinetic-energydistribution over the modes, and the correlation between the number of the modes and the mean kinetic energyof the cluster are distinguished.
