High precision determination of the melting points of water TIP4P/2005 and water TIP4P/Ice models by the direct coexistence technique

Abstract

An exhaustive study by molecular dynamics has been performed to analyze the factors that enhance the precision of the technique of direct coexistence for a system of ice and liquid water. The factors analyzed are the stochastic nature of the method, the finite size effects, and the influence of the initial ice configuration used. The results obtained show that the precision of estimates obtained through the technique of direct coexistence is markedly affected by the effects of finite size, requiring systems with a large number of molecules to reduce the error bar of the melting point. This increase in size causes an increase in the simulation time, but the estimate of the melting point with a great accuracy is important, for example, in studies on the ice surface. We also verified that the choice of the initial ice I configuration with different proton arrangements does not significantly affect the estimate of the melting point. Importantly this study leads us to estimate the melting point at ambient pressure of two of the most popular models of water, TIP4P/2005 and TIP4P/Ice, with the greatest precision to date.

A Bayesian approach for identification of ice Ih, ice Ic, high density, and low density liquid water with a torsional order parameter

“…The temperature of an ice structure is elevated to 400 K with fixing the volume to melt it, and then it is annealed at a constant pressure, 1 bar, to obtain the liquid structures of target temperatures. The melting point of TIP4P/2005 water is 250 K. 33 The distributions for liquid water at the melting point, Tm, is similar to that at Tm + 30 K: there is a peak at C = 0 and CC = 0, where C and CC are the real and imaginary parts of , respectively. This peak, however, becomes less pronounced in supercooled water at Tm -30 K and Tm -60 K. There are two peaks in the distribution for ice Ih.…”

Spontaneous NaCl-doped ices Ih, Ic, III, V and VI. Understanding the mechanism of ion inclusion and its dependence on the crystalline structure of ice

“…For our study, we will consider the equilibrium temperature for each ice phase obtained by simulation from the works of Conde et al 24,25 and Zaragoza et al 26 using the TIP4P/2005 water model. This model correctly describes many of the properties of water, including a qualitative description of the phase diagram.…”

“…The last step consists of the assembly of both phases and a final short equilibration run (20 ps) to have equilibrium at the interface before starting the brine rejection simulations. All systems are formed by a slab of ice which acts as a seed crystal in contact with a liquid water phase containing Table 1 Melting temperatures as obtained from direct coexistence simulations by Conde et al 24,25 for the ices I h , III, V and VI, and by Zaragoza et al 26 Phys. Chem.…”

Melting Points of OPC and OPC3 Water Models

“…Fortunately, it was shown earlier that the initial ice configuration with different proton arrangements does not significantly affect the estimate of the melting point. 23 We note that as the ice is being heated in the simulation, a certain amount of disorder is introduced naturally.…”

“…A recent study on the direct coexistence method by Conde et al 23 has shown that the accuracy (error bar size) of the calculated melting point is affected by the simulation box size. Here, we chose the box size of 3456 (liquid) + 3456 (solid) water molecules for all the four water models calculated in this work, which according to Conde’s study, results in a reasonable accuracy of ∼1 K error bar for a four-point water model.…”