Department of Chemistry, University of Oregon, Eugene, Oregon 97403, United States.
J Phys Chem A. 2011 Apr 28;115(16):3980-9. doi: 10.1021/jp108921x. Epub 2011 Apr 4.
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.
最近提出的一种用于小分子内部核动力学和低温宿主介质诱导的小振幅相干运动的量子/半经典处理方法（Chapman，CT；Cina，JA J.Chem.Phys.2007，127，114502）进一步进行了分析，并对其数值实现进行了初步测试。在与一维介质相互作用的一维系统的说明性背景下，我们重新推导了定义伴随量子力学系统的每个能量本征态的高斯波包的参数的固定振动基/高斯浴（FVB/GB）运动方程。高斯浴近似的有效性条件与支持近似粒子数守恒的条件一致。我们对 FVB/GB 方案进行了初步的数值测试，并通过将其预测与高频系统与低频浴振荡器线性耦合的二次谐波振荡器的精确结果进行比较，说明了它为介质中的相干运动提供的半经典描述。在 FVB/GB 框架内，很容易且准确地计算线性振子吸收光谱或等效的超快波包干涉测量信号。
