On the accuracy of the MB-pol many-body potential for water: Interaction energies, vibrational frequencies, and classical thermodynamic and dynamical properties from clusters to liquid water and ice
Sandeep K. Reddy, Shelby C. Straight, Pushp Bajaj, C. Huy Pham, Marc Riera, Daniel R. Moberg, Miguel A. Morales, Chris Knight, Andreas W. Gotz, Francesco Paesani
The MB-pol many-body potential has recently emerged as an accurate molecular model for water simulations from the gas to the condensed phase. In this study, the accuracy of MB-pol is systematically assessed across the three phases of water through extensive comparisons with experimental data and high-level ab initio calculations. Individual many-body contributions to the interaction energies as well as vibrational spectra of water clusters calculated with MB-pol are in excellent agreement with reference data obtained at the coupled cluster level. Several structural, thermodynamic, and dynamical properties of the liquid phase at atmospheric pressure are investigated through classical molecular dynamics simulations as a function of temperature. The structural properties of the liquid phase are in nearly quantitative agreement with X-ray diffraction data available over the temperature range from 268 to 368 K. The analysis of other thermodynamic and dynamical quantities emphasizes the importance of explicitly including nuclear quantum effects in the simulations, especially at low temperature, for a physically correct description of the properties of liquid water. Furthermore, both densities and lattice energies of several ice phases are also correctly reproduced by MB-pol. Following a recent study of DFT models for water, a score is assigned to each computed property, which demonstrates the high and, in many respects, unprecedented accuracy of MB-pol in representing all three phases of water.
The vibrational properties of benzene on an ordered water ice surface
本文提出了一种CCSD（T）+PBE-D3混合方法来计算气相苯和苯吸附在有序水-冰表面的振动特征。我们比较我们的方法对实验记录的光谱和计算使用PBE-D3的方法（谐波和非谐波）的结果。计算使用质子有序XIh水冰表面组成的288个水分子，并与实验记录的ASW冰表面的光谱结果进行比较。我们显示的重要性，包括水冰表面光谱计算，由于所得的振动模式，频率和强度的红外光谱中看到的过渡。的整体强度图案转移从一个占主导地位的$ν_{11}$带在气相中的几个高强度载体的红外光谱的吸附苯。当用于吸附苯时，本文提出的混合方法实现了21 cm $^{-1}$的IR活性模式的RMSD，而非谐波和谐波PBE-D3方法分别为72 cm $^{-1}$和49 cm $^{-1}$。与实验相比，我们的气态苯混合模型也获得了最佳结果，与非谐波和谐波PBE-D3方法的55 cm $^{-1}$和31 cm $^{-1}$相比，IR活性模式的RMSD为24 cm $^{-1}$。为了便于分配，我们生成并提供了一个对应关系图的正常模式的气体和吸附的苯分子。最后，我们计算的频率偏移，$Δν$，吸附苯相对于其气相突出的表面相互作用对振动带的影响，并评估我们选择的色散校正密度泛函理论的适用性。
Consiglio Nazionale delle Ricerche, Istituto di Fisica Applicata ‘Nello Carrara’（意大利国家研究委员会，内洛·卡拉拉应用物理研究所）；ISIS Neutron and Muon Source, STFC Rutherford Appleton Laboratory（ISIS中子与μ子源，STFC卢瑟福阿普尔顿实验室）；Università degli Studi di Pisa（比萨大学）；Consiglio Nazionale delle Ricerche, Istituto Nazionale di Ottica（意大利国家研究委员会，国家光学研究所）
Accurate Machine Learning Interatomic Potentials for Polyacene Molecular Crystals: Application to Single Molecule Host-Guest Systems
Max Planck Institute for the Structure and Dynamics of Matter（马克斯·普朗克固体研究和光谱学研究所）；Center for Free-Electron Laser Science（自由电子激光科学中心）；Initiative for Computational Catalysis (ICC)（计算催化倡议）；The Flatiron Institute（平顿研究所）
The $ω^3$ scaling of the vibrational density of states in quasi-2D nanoconfined solids
原子振动在各种物理、化学和生物系统的功能中起着至关重要的作用。Debye理论很好地描述了晶体块体材料的振动性质和比热，它在很少的基本假设下成功地预言了块体有序固体振动态密度（VDOS）的二次$ω^{2}$低频标度。然而，自由度更少的纳米限制材料的类似框架还远没有得到很好的探索。使用非弹性中子散射，我们的特点是VDOS的无定形冰局限于一个厚度为$\approx 1$ nm的氧化石墨烯膜内，我们观察到一个交叉从德拜$ω^2$缩放到一个异常的$ω^3$行为时，减少限制大小$L$。此外，使用分子动力学模拟，我们证实了实验结果，也证明了这样的缩放的VDOS出现在晶体和非晶态固体板约束下。我们从理论上证明了这种低频$ω^3$定律是由沿一个空间方向的约束引起的动量相空间的几何约束引起的。最后，我们预测，德拜标度再现在一个特征频率$ω_\times= v L/2π$，与$v$的材料的声速，我们证实了这一定量估计与模拟。通过结合理论，实验和模拟结果揭示的这种新的物理现象与合成和生物背景下的无数系统有关，它可能会影响纳米器件或薄膜等受限系统的各种技术应用。
