Department of Physics, Brooklyn College of the City University of New York, Brooklyn, New York 11210, United States.
Ph.D. Program in Physics, The Graduate Center of the City University of New York, New York, New York 10016, United States.
J Phys Chem B. 2023 May 25;127(20):4633-4645. doi: 10.1021/acs.jpcb.3c01025. Epub 2023 May 13.
We study the nuclear quantum effects (NQE) on the thermodynamic properties of low-density amorphous ice (LDA) and hexagonal ice () at = 0.1 MPa and ≥ 25 K. Our results are based on path-integral molecular dynamics (PIMD) and classical MD simulations of HO and DO using the q-TIP4P/F water model. We show that the inclusion of NQE is necessary to reproduce the experimental properties of LDA and ice . While MD simulations (no NQE) predict that the density ρ() of LDA and ice increases monotonically upon cooling, PIMD simulations indicate the presence of a density maximum in LDA and ice . MD and PIMD simulations also predict a qualitatively different T-dependence for the thermal expansion coefficient α() and bulk modulus () of both LDA and ice . Remarkably, the ρ(), α(), and () of LDA are practically identical to those of ice . The origin of the observed NQE is due to the delocalization of the H atoms, which is identical in LDA and ice . H atoms delocalize considerably (over a distance ≈ 20-25% of the OH covalent-bond length) and anisotropically (preferentially perpendicular to the OH covalent bond), leading to less linear hydrogen bonds HB (larger HOO angles and longer OO separations) than observed in classical MD simulations.
我们研究了在 = 0.1 MPa 和 ≥ 25 K 下低密非晶冰 (LDA) 和六方冰 () 的热力学性质中的核量子效应 (NQE)。我们的结果基于使用 q-TIP4P/F 水模型的 HO 和 DO 的路径积分分子动力学 (PIMD) 和经典 MD 模拟。我们表明，为了重现 LDA 和冰的实验性质，必须包含 NQE。虽然 MD 模拟 (无 NQE) 预测 LDA 和冰的密度 ρ()随着冷却而单调增加，但 PIMD 模拟表明 LDA 和冰中存在密度最大值。MD 和 PIMD 模拟还预测了 LDA 和冰的热膨胀系数 α()和体弹性模量 () 的 T 依赖性定性不同。值得注意的是，LDA 的 ρ()、α()和 () 几乎与冰的相同。观察到的 NQE 的起源是由于 H 原子的离域，这在 LDA 和冰中是相同的。H 原子离域相当大（在 OH 共价键长度的约 20-25%的距离上）且各向异性（优先垂直于 OH 共价键），导致比经典 MD 模拟中观察到的更少的线性氢键 HB（更大的 HOO 角和更长的 OO 分离）。
