Abstract
Thermal motion of CH is investigated by performing an ab initio molecular dynamics method with the second‐order Møller‐Plesset (MP2)/6‐311G** force field. In the trajectories obtained at 400 K, we have observed rapid interconversion behavior of the geometrical parameters of CH with the frequency of 0.6/ps, where the CH pair forming the small angle around 55° is switched to another pair on subpicosecond time scale. The switching patterns are found to be classified into the following two types. Type 1: one CH of the small angled CH pair is switched to one CH of the other CH pair. Type 2: the small angled CH pair is switched to the other CH pair, which has been newly observed in the present ab initio MD calculation. The four CH bonds of CH are characterized by the long and short CH bonds in a time region of the trajectories, and also for the time‐evolution of CH bonds such interconversion behavior is observed. The switching patterns of the geometrical parameters are compared with those in the interconversion scheme between six equivalent C~2v~ symmetry structures of CH [Paddon‐Row, M. N. et al., J Am Chem Soc 1985, 107, 7696]. We have also investigated the electronic energy fluctuation due to thermal motion of CH. The standard deviation of total electronic energy at 400 K is evaluated to be 1.2 kcal/mol. © 2004 Wiley Periodicals, Inc. J Comput Chem 15: 1910–1919, 2004