ABSTRACT

Car–Parrinello molecular dynamics simulations were applied to investigate phase-transition behavior of (H${}_2$O)${}_n$ few-body system for n=1−4 at BLYP-GGA level of density-functional theory. A number of important indicators including Lindemann index, ionic mean square displacements, radial distribution function, and shape deformation parameter were accordingly calculated as functions of temperature from 5 to 2000 K. All the four systems exhibited high thermal stabilities compared to bulk water with melting points estimated at $T_m=1200,950$, and 700 K for n=2,3, and 4, respectively. No obvious melting behavior was also observed for n=1 due to strong O–H covalent bonds. These $T_m$ values were also found to obey a decreasing trend as the size of the system increases, showing that a minimum size value can also be estimated for which characteristics of liquid water at the thermodynamic limit would consequently appear, in case of studying larger systems with $n\gg 4$.

摘要

Car-Parrinello 分子动力学模拟被应用于研究 (H${}_2$哦）${}_n$在密度泛函理论的 BLYP-GGA 水平上n = 1−4 的少体系统。包括林德曼指数、离子均方位移、径向分布函数和形状变形参数在内的许多重要指标被相应地计算为 5 到 2000 K 温度的函数。与具有熔点的散装水相比，所有四种系统都表现出较高的热稳定性估计在${吨}_{米}=1200,950$和 700 K ，分别为n = 2,3 和 4。由于强的 O-H 共价键，在n = 1时也没有观察到明显的熔化行为。这些${吨}_{米}$ 还发现随着系统规模的增加，这些值遵循减小的趋势，这表明在研究具有热力学极限的液态水的特征时，也可以估计最小尺寸值。 $n\gg 4$.