Eltareb Ali, Lopez Gustavo E, Giovambattista Nicolas
Department of Physics, Brooklyn College of the City University of New York, Brooklyn, New York 11210, USA.
Department of Chemistry, Lehman College of the City University of New York, Bronx, New York 10468, USA.
J Chem Phys. 2022 May 28;156(20):204502. doi: 10.1063/5.0087680.
We perform path integral molecular dynamics (PIMD) simulations of a monatomic liquid that exhibits a liquid-liquid phase transition and liquid-liquid critical point. PIMD simulations are performed using different values of Planck's constant h, allowing us to study the behavior of the liquid as nuclear quantum effects (NQE, i.e., atoms delocalization) are introduced, from the classical liquid (h = 0) to increasingly quantum liquids (h > 0). By combining the PIMD simulations with the ring-polymer molecular dynamics method, we also explore the dynamics of the classical and quantum liquids. We find that (i) the glass transition temperature of the low-density liquid (LDL) is anomalous, i.e., T (P) decreases upon compression. Instead, (ii) the glass transition temperature of the high-density liquid (HDL) is normal, i.e., T (P) increases upon compression. (iii) NQE shift both T (P) and T (P) toward lower temperatures, but NQE are more pronounced on HDL. We also study the glass behavior of the ring-polymer systems associated with the quantum liquids studied (via the path-integral formulation of statistical mechanics). There are two glass states in all the systems studied, low-density amorphous ice (LDA) and high-density amorphous ice (HDA), which are the glass counterparts of LDL and HDL. In all cases, the pressure-induced LDA-HDA transformation is sharp, reminiscent of a first-order phase transition. In the low-quantum regime, the LDA-HDA transformation is reversible, with identical LDA forms before compression and after decompression. However, in the high-quantum regime, the atoms become more delocalized in the final LDA than in the initial LDA, raising questions on the reversibility of the LDA-HDA transformation.
我们对一种呈现液 - 液相转变和液 - 液临界点的单原子液体进行了路径积分分子动力学（PIMD）模拟。使用不同的普朗克常数h值进行PIMD模拟，这使我们能够研究从经典液体（h = 0）到量子特性逐渐增强的液体（h > 0）引入核量子效应（NQE，即原子离域）时液体的行为。通过将PIMD模拟与环聚合物分子动力学方法相结合，我们还探究了经典液体和量子液体的动力学。我们发现：（i）低密度液体（LDL）的玻璃化转变温度异常，即T（P）在压缩时降低。相反，（ii）高密度液体（HDL）的玻璃化转变温度正常，即T（P）在压缩时升高。（iii）NQE使T（P）和T（P）都向更低温度移动，但NQE在HDL上更为显著。我们还研究了与所研究的量子液体相关的环聚合物系统的玻璃行为（通过统计力学的路径积分形式）。在所研究的所有系统中存在两种玻璃态，低密度非晶冰（LDA）和高密度非晶冰（HDA），它们分别是LDL和HDL的玻璃对应物。在所有情况下，压力诱导的LDA - HDA转变都是急剧的，类似于一级相变。在低量子区域，LDA - HDA转变是可逆的，压缩前和减压后的LDA形式相同。然而，在高量子区域，最终LDA中的原子比初始LDA中的原子离域程度更高，这引发了关于LDA - HDA转变可逆性的问题。
