小仲氢团簇中的OCS：N=1-8络合氢分子的能量和结构
OCS in small para-hydrogen clusters: energetics and structure with N=1-8 complexed hydrogen molecules
摘要：
我们用零温量子蒙特卡罗方法研究了线性OCS分子与少量仲氢分子（N=1-8）形成的复合物的结构和能量。基态计算采用重要抽样刚体扩散蒙特卡罗（IS-RBDMC）方法，激发态计算采用投影算子虚时谱演化（POITSE）方法.的基态被发现是高度结构化的，随着N增加到8逐渐建立两个轴向环。OCS分子周围的方位角密度相关性的分析表明，这些环是相当离域的小N值，但成为强烈本地化的N \geq 5。激发态计算的总集群角动量值和旋转能级的范围内拟合，以获得作为集群大小N的函数的复杂的OCS分子的有效旋转和畸变常数。对这些光谱常数的详细分析表明，OCS与仲氢的复合物在动力学行为上具有异常丰富的变化，尺寸N=1-2显示出接近刚性的行为，尺寸N=3-4显示出极其松软的行为，并且较大尺寸N=5-8再次显示出更刚性的行为。N=3-4时获得的畸变常数D的大值是合理的OCS旋转和第一个部分填充的仲氢分子环的“呼吸”模式之间的耦合。
英文摘要：
We determine the structure and energetics of complexes of the linear OCS molecule with small numbers of para-hydrogen molecules, N=1-8, using zero temperature quantum Monte Carlo methods. Ground state calculations are carried out with importance-sampled rigid body diffusion Monte Carlo (IS-RBDMC) and excited state calculations with the projection operator imaginary time spectral evolution (POITSE) methodology. The ground states are found to be highly structured, with a gradual build up of two axial rings as N increases to 8. Analysis of the azimuthal density correlations around the OCS molecule shows that these rings are quite delocalized for small N values, but become strongly localized for N \geq 5 . Excited state calculations are made for a range of total cluster angular momentum values and the rotational energy levels fitted to obtain effective rotational and distortion constants of the complexed OCS molecule as a function of cluster size N. Detailed analysis of these spectroscopic constants indicates that the complexes of OCS with para-hydrogen have an unusually rich variation in dynamical behavior, with sizes N=1-2 showing near rigid behavior, sizes N=3-4 showing extremely floppy behavior, and the larger sizes N=5-8 showing more rigid behavior again. The large values of the distortion constant D obtained for N=3-4 are rationalized in terms of the coupling between the OCS rotations and the "breathing" mode of the first, partially filled ring of para-hydrogen molecules.
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