Polok Kamil
Department of Chemistry, University of Warsaw , Zwirki i Wigury 101, 02-089 Warsaw, Poland.
J Phys Chem B. 2018 Feb 8;122(5):1638-1654. doi: 10.1021/acs.jpcb.7b08724. Epub 2018 Jan 26.
Recently polarizable force fields are becoming increasingly popular for molecular dynamics simulations. As the signal obtained in the optical Kerr effect (OKE) experiment is due to the polarizability dynamics of the investigated system, a study is conducted in order to compare the experimental results with those obtained with the polarizable AMOEBA force field. The comparison is made in the frequency domain; however, time domain data are also included. The selected molecular systems are the isotropic carbon tetrachloride molecule, the anisotropic chloroform, carbon disulfide and acetone molecules, and the hydrogen-bonded water and methanol molecules. Different dipole-induced-dipole (DID) method variants are used for calculation of the OKE response, showing the importance of use of the all-atom approach with preoptimized atomic polarizabilities. In order to obtain a good intermolecular to intramolecular components amplitude ratio, the isotropic polarizability in the Thole correction needs to be updated between iterations. The convergence of the spectra calculated with different DID variants is also considered, and the approach that appears to be the best gives a very good approximation after three iterations. The comparison of the experimental and simulated spectra shows a rather good agreement for the non-hydrogen-bonded molecules, although the contribution of the reorientation of anisotropic molecules is overestimated. In the case of the hydrogen-bonded molecules, the theoretical spectra are far from the experimental ones. The highly overestimated librational bands indicate excessive polarizability anisotropy introduced by the potential model. Finally, in order to verify the significance of different components of the AMOEBA model, it is gradually simplified and compared with a simple reference potential model. Removal of polarizability shows a tremendous change in the case of hydrogen-bonded liquids, whereas for the other molecules it is of minor importance. The non-hydrogen-bonded liquids are, however, more sensitive to the presence of atomic multipoles in the model.
最近，可极化力场在分子动力学模拟中越来越受欢迎。由于光学克尔效应（OKE）实验中获得的信号源于被研究系统的极化率动力学，因此开展了一项研究，以便将实验结果与使用可极化AMOEBA力场获得的结果进行比较。比较是在频域中进行的；不过也包含了时域数据。所选的分子体系有各向同性的四氯化碳分子、各向异性的氯仿、二硫化碳和丙酮分子，以及形成氢键的水和甲醇分子。使用了不同的偶极诱导偶极（DID）方法变体来计算OKE响应，这表明使用具有预优化原子极化率的全原子方法的重要性。为了获得良好的分子间与分子内成分振幅比，在迭代之间需要更新Thole校正中的各向同性极化率。还考虑了用不同DID变体计算的光谱的收敛性，经过三次迭代后，表现最佳的方法能给出非常好的近似值。实验光谱与模拟光谱的比较表明，对于非氢键分子，两者相当吻合，尽管各向异性分子重取向的贡献被高估了。对于氢键分子，理论光谱与实验光谱相差甚远。高度高估的振动带表明势模型引入了过大的极化率各向异性。最后，为了验证AMOEBA模型不同组分的重要性，对其进行逐步简化，并与一个简单的参考势模型进行比较。去除极化率后，氢键液体的情况发生了巨大变化，而对于其他分子来说则不太重要。然而，非氢键液体对模型中原子多极矩的存在更为敏感。
