Constructing simple yet accurate potentials for describing the solvation of HCl/water clusters in bulk helium and nanodroplets
Constructing simple yet accurate potentials for describing the solvation of HCl/water clusters in bulk helium and nanodroplets
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DOI：
10.1039/c1cp20991d
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发表时间：
2011-01-01
影响因子：
3.3
通讯作者：
Jansen, Georg
中科院分区：
文献类型：
--
作者：
Boese, A. Daniel;Forbert, Harald;Jansen, Georg
溶解在超流氦簇中的分子、复合物和分子聚集体的红外光谱，通常称为氦纳米液滴隔离 (HENDI) 光谱，是一种成熟的、强大的实验技术，用于在超低温下提取高分辨率旋转振动光谱。此类系统的真实量子模拟，特别是在溶质正在进行化学反应的情况下，需要精确的溶质-氦势，并且该势也足够简单，可以在典型的蒙特卡罗或分子动力学采样中所需的大量步骤中进行有效评估。这排除了在高分辨率光谱研究领域中使用通常参数化的小型复合物的全局势能表面，鉴于所施加的计算量，这些表面集中于刚性分子与氦的分子间相互作用。另一方面，简单的类 Lennard-Jones 对势无法提供所需的灵活性和准确性来解释溶质分子的化学反应。在这里，提出了构建足够精确的位点势以用于典型量子模拟的一般方案。该方案采用基于原子的网格，考虑了局部和全局最小值，并应用于被氦溶剂化的 HCl(H2O)(4) 簇的特殊情况。第一步，使用密度泛函理论和对称适应扰动理论的有效组合（即 DFT-SAPT 方法）计算氦原子与从 HCl(H2O)(4) 团簇解离后的轨迹采样的一组代表性构型的精确相互作用能。对于每个采样的簇结构，氦原子被放置在分布在空间中的数百个位置，导致总数约为 400 000 次此类量子化学计算。由此产生的总相互作用能分解为几个能量贡献，用于拟合位点势，其中位点位于原子位置，此外，伪位点沿着分子簇内原子位点对的连接线分布。这种方法确保该溶质-氦电势能够描述未离解的分子和离解的（两性）离子构型，以及互连反应路径，而无需根据特定构型重新调整部分电荷或其他参数。较大的 HCl(H2O)(5) 簇与氦相互作用的测试计算证明了导出的位点电势的可转移性。这种特定电势可以很容易地用于散装氦或氦纳米液滴中的 HCl/水簇的量子模拟，而基础构建过程可以推广到其他原子溶剂中的其他分子溶质，例如稀有气体基质隔离光谱中遇到的分子溶质。
The infrared spectroscopy of molecules, complexes, and molecular aggregates dissolved in superfluid helium clusters, commonly called HElium NanoDroplet Isolation (HENDI) spectroscopy, is an established, powerful experimental technique for extracting high resolution ro-vibrational spectra at ultra-low temperatures. Realistic quantum simulations of such systems, in particular in cases where the solute is undergoing a chemical reaction, require accurate solute-helium potentials which are also simple enough to be efficiently evaluated over the vast number of steps required in typical Monte Carlo or molecular dynamics sampling. This precludes using global potential energy surfaces as often parameterized for small complexes in the realm of high-resolution spectroscopic investigations that, in view of the computational effort imposed, are focused on the intermolecular interaction of rigid molecules with helium. Simple Lennard-Jones-like pair potentials, on the other hand, fall short in providing the required flexibility and accuracy in order to account for chemical reactions of the solute molecule. Here, a general scheme of constructing sufficiently accurate site-site potentials for use in typical quantum simulations is presented. This scheme employs atom-based grids, accounts for local and global minima, and is applied to the special case of a HCl(H2O)(4) cluster solvated by helium. As a first step, accurate interaction energies of a helium atom with a set of representative configurations sampled from a trajectory following the dissociation of the HCl(H2O)(4) cluster were computed using an efficient combination of density functional theory and symmetry-adapted perturbation theory, i.e. the DFT-SAPT approach. For each of the sampled cluster configurations, a helium atom was placed at several hundred positions distributed in space, leading to an overall number of about 400 000 such quantum chemical calculations. The resulting total interaction energies, decomposed into several energetic contributions, served to fit a site-site potential, where the sites are located at the atomic positions and, additionally, pseudo-sites are distributed along the lines joining pairs of atom sites within the molecular cluster. This approach ensures that this solute-helium potential is able to describe both undissociated molecular and dissociated (zwitter-) ionic configurations, as well as the interconnecting reaction pathway without re-adjusting partial charges or other parameters depending on the particular configuration. Test calculations of the larger HCl(H2O)(5) cluster interacting with helium demonstrate the transferability of the derived site-site potential. This specific potential can be readily used in quantum simulations of such HCl/water clusters in bulk helium or helium nanodroplets, whereas the underlying construction procedure can be generalized to other molecular solutes in other atomic solvents such as those encountered in rare gas matrix isolation spectroscopy.