Instituto de Fisica Fundamental, C.S.I.C., Serrano 123, 28006 Madrid, Spain.
J Phys Chem A. 2009 Dec 31;113(52):14718-29. doi: 10.1021/jp9048583.
The structure and energetics of (3,4)HeCs(2)((3)Sigma(u)) molecules are analyzed from first principles. Fixing the cesium dimer at its equilibrium distance, the electronic structure was determined through ab initio methods at the CCSD(T) level of theory using a large basis set to compute the interaction energies. At the T-shaped geometry, there is a shallow well with a depth of approximately 2 cm(-1) placed at R approximately 6.75 A, R being the distance from the center of mass of Cs(2) to He. That depth gradually decreases to approximately 0.75 cm(-1), while R increases to about 11.5 A at linear arrangements. A simple model of adding atom-atom Lennard-Jones potentials with well-depth and equilibrium distance parameters depending on the angular orientation was found to accurately reproduce the ab initio points. Using this analytical form, variational calculations at zero total angular momentum are performed, predicting a single bound level at approximately -0.106 (approximately -0.042) cm(-1) for the boson (fermion) species. Further calculations using Quantum Monte Carlo methods are carried out and found to be in good agreement with the variational ones. On the basis of the present results, such analytical expression could in turn be used to describe the structure and binding of larger complexes and therefore opens the possibility to further studies involving such aggregates.
从第一性原理分析了 (3,4)HeCs(2)((3)Sigma(u)) 分子的结构和能量。将铯二聚体固定在其平衡距离处，通过从头算方法在 CCSD(T)理论水平上使用大基组确定了电子结构，以计算相互作用能。在 T 形几何形状中，存在一个浅势阱，其深度约为 2 cm(-1)，位于 R 约为 6.75 A，其中 R 是 Cs(2)到 He 质心的距离。随着 R 增加到约 11.5 A，深度逐渐减小到约 0.75 cm(-1)。对于线性排列，发现添加原子-原子 Lennard-Jones 势能的简单模型具有取决于角取向的阱深和平衡距离参数，可以准确地再现从头算点。使用这种分析形式，在总角动量为零的情况下进行变分计算，预测玻色子（费米子）物种的单个束缚能级约为 -0.106（约 -0.042）cm(-1)。进一步使用量子蒙特卡罗方法进行计算，发现与变分计算结果吻合良好。基于目前的结果，这种分析表达式反过来可以用于描述更大复合物的结构和结合，从而为进一步研究此类聚集体开辟了可能性。
