Analytic dynamics of the Morse oscillator derived by semiclassical closures.

The quantized Hamilton dynamics methodology [O. V. Prezhdo and Y. V. Pereverzev, J. Chem. Phys. 113, 6557 (2000)] is applied to the dynamics of the Morse potential using the SU(2) ladder operators. A number of closed analytic approximations are derived in the Heisenberg representation by performing semiclassical closures and using both exact and approximate correspondence between the ladder and position-momentum variables. In particular, analytic solutions are given for the exact classical dynamics of the Morse potential as well as a second-order semiclassical approximation to the quantum dynamics. The analytic approximations are illustrated with the O-H stretch of water and a Xe-Xe dimer. The results are extended further to coupled Morse oscillators representing a linear triatomic molecule. The reported analytic expressions can be used to accelerate classical molecular dynamics simulations of systems containing Morse interactions and to capture quantum-mechanical effects.