title: Numerical tests of a fixed vibrational basis/gaussian bath theory for small molecule dynamics in low-temperature media.
abstract: A recently framed quantum/semiclassical treatment for the internal nuclear dynamics of a small molecule and the induced small-amplitude coherent motion of a low-temperature host medium (Chapman, C. T.; Cina, J. A. J. Chem. Phys.2007,127, 114502) is further analyzed and subjected to initial tests of its numerical implementation. In the illustrative context of a 1D system interacting with a 1D medium, we rederive the fixed vibrational basis/gaussian bath (FVB/GB) equations of motion for the parameters defining the gaussian bath wave packet accompanying each of the energy eigenkets of the quantum mechanical system. The conditions of validity for the gaussian-bath approximation are shown to coincide with those supporting approximate population conservation. We perform initial numerical tests of the FVB/GB scheme and illustrate the semiclassical description it provides of coherent motion in the medium by comparing its predictions with the exact results for a high-frequency system harmonic oscillator bilinearly coupled to a lower-frequency bath oscillator. Linear vibronic absorption spectra or, equivalently, ultrafast wave packet interferometry signals are shown to be readily and accurately calculable within the FVB/GB framework.
authors.affiliation: Department of Chemistry, University of Oregon, Eugene, Oregon 97403, United States.
authors.forename: Craig T
authors.initials: CT
authors.lastname: Chapman
authors.forename: Xiaolu
authors.initials: X
authors.lastname: Cheng
authors.forename: Jeffrey A
authors.initials: JA
authors.lastname: Cina
mesh_terms: D011789:Quantum Theory; D013696:Temperature; D014732:Vibration