School of Physics and Astronomy, The University of Manchester, Manchester, M13 9PL, United Kingdom.
J Chem Phys. 2012 Jul 28;137(4):044504. doi: 10.1063/1.4736853.
It is a well recognized difficult task to simulate the vibrational dynamics of ices using the density functional theory (DFT), and there has thus been rather limited success in modelling the inelastic neutron scattering (INS) spectra for even the simplest structure of ice, ice Ih, particularly in the translational region below 400 cm(-1). The reason is partly due to the complex nature of hydrogen bonding (H-bond) among water-water molecules which require considerable improvement of the quantum mechanical simulation methods, and partly owing to the randomness of protons in ice structures which often requires simulation of large super-lattices. In this report, we present the first series of successful simulation results for ice Ih using DFT methods. On the basis of the recent advancement in the DFT programs, we have achieved for the first time theoretical outcomes that not only reproduce the rotational frequencies between 500 to 1200 cm(-1) for ice Ih, but also the two optic peaks at ∼240 and 320 cm(-1) in the translational region of the INS spectra [J. C. Li, J. Chem. Phys 105, 6733 (1996)]. Besides, we have also investigated the impact of pairwise configurations of H(2)O molecules on the H-bond and found that different proton arrangements of pairwise H(2)O in the ice Ih crystal lattice could not alter the nature of H-bond as significantly as suggested in an early paper [J. C. Li and D. K. Ross, Nature (London) 365, 327 (1993)], i.e., reproducing the two experimental optic peaks do not need to invoke the two H-bonds as proposed in the previous model which led to considerable debates. The results of this work suggest that the observed optic peaks may be attributed to the coupling between the two bands of H-O stretching modes in H(2)O. The current computational work is expected to shed new light on the nature of the H-bonds in water, and in addition to offer a new approach towards probing the interaction between water and biomaterials for which H-bond is essential.
使用密度泛函理论（DFT）模拟冰的振动动力学是一项公认的艰巨任务，因此，即使对于冰的最简单结构冰 Ih，也只能在低于 400 cm(-1)的平移区域内对非弹性中子散射（INS）光谱进行建模，取得了相当有限的成功。原因部分在于水分子之间氢键（H-bond）的复杂性质，这需要对量子力学模拟方法进行大量改进，部分原因在于冰结构中质子的随机性，这通常需要模拟大超晶格。在本报告中，我们首次成功使用 DFT 方法模拟冰 Ih。基于 DFT 程序的最新进展，我们首次实现了理论结果，不仅再现了冰 Ih 之间 500 至 1200 cm(-1)的旋转频率，而且再现了 INS 光谱平移区的两个光学峰在约 240 和 320 cm(-1)。此外，我们还研究了 H(2)O 分子的成对构型对 H-bond 的影响，发现冰 Ih 晶格中成对 H(2)O 的不同质子排列不会像早期一篇论文中所建议的那样显著改变 H-bond 的性质[J. C. Li 和 D. K. Ross，《自然》（伦敦）365, 327 (1993)]，即再现两个实验光学峰不需要像之前的模型那样引入两个 H-bond，这导致了大量的争论。这项工作的结果表明，观察到的光学峰可能归因于 H(2)O 中两个 H-O 伸缩模式带之间的耦合。目前的计算工作有望为水的 H-bond 性质提供新的认识，并为探测水与生物材料之间的相互作用提供新的方法，而 H-bond 对生物材料至关重要。
