Comparison of the structure of harmonic aqueous glasses and liquid water

We report computer simulation results of free energies of proton-disordered hexagonal ice and liquid water at atmospheric pressure with the 4-site transferable intermolecular potential model of water. A new reference system is used to calculate the free energy of the ice phase. The melting point of proton-disordered hexagonal ice at atmospheric pressure is found to be T m ϭ238 (Ϯ7) K. This result is consistent with a previous estimation, 230 KϽT m Ͻ250 K, from molecular dynamic simulation of the surface melting of the proton-disordered hexagonal ice ͓G.-J. Kroes, Surf. Sci. 275, 365 ͑1992͔͒.

Section: Model and Methodsmentioning

confidence: 99%

The melting temperature of proton-disordered hexagonal ice: A computer simulation of 4-site transferable intermolecular potential model of water

Gao

Zeng

Tanaka

2000

“…In the harmonic approximation, one approximates the normal modes of the system to be a set of 3N harmonic oscillators, so that the partition function Q can be expressed in term of the partition function q i for the individual modes. 15 For a continuous distribution of normal modes, the partition function Q can be shown to be related to DoS(v) by 15,16 ln…”

Section: Application To Single-particle Homogenous Liquidsmentioning

confidence: 99%

On the absolute thermodynamics of water from computer simulations: A comparison of first-principles molecular dynamics, reactive and empirical force fields

Pascal

Schärf

Jung

et al. 2012

We present the absolute enthalpy, entropy, heat capacity, and free energy of liquid water at ambient conditions calculated by the two-phase thermodynamic method applied to ab initio, reactive and classical molecular dynamics simulations. We find that the absolute entropy and heat capacity of liquid water from ab initio molecular dynamics (AIMD) is underestimated, but falls within the range of the flexible empirical as well as the reactive force fields. The origin of the low absolute entropy of liquid water from AIMD simulations is due to an underestimation of the translational entropy by 20% and the rotational entropy by 40% compared to the TIP3P classical water model, consistent with previous studies that reports low diffusivity and increased ordering of liquid water from AIMD simulations. Classical MD simulations with rigid water models tend to be in better agreement with experiment (in particular TIP3P yielding the best agreement), although the TIP4P-ice water model, the only empirical force field that reproduces the experimental melting temperature, has the lowest entropy, perhaps expectedly. This reiterates the limitations of existing empirical water models in simultaneously capturing the thermodynamics of solid and liquid phases. We find that the quantum corrections to heat capacity of water can be as large as 60%. Although certain water models are computed to yield good absolute free energies of water compared to experiments, they are often due to the fortuitous enthalpy-entropy cancellation, but not necessarily due to the correct descriptions of enthalpy and entropy separately.

“…26 The optimized structures for every water model were obtained with the steepest-descent method. Zero-point vibration energy 4,27 was evaluated using normal-mode analysis, but only for TIP5P and SPC/E models. The vibration energy was then added to the potential energy of the corresponding optimized water cluster structure.…”

mentioning

confidence: 99%

Ab initio studies of quasi-one-dimensional pentagon and hexagon ice nanotubes

Bai

Parra

et al. 2003

Ab initio plane-wave total-energy calcuation is carried out to study the relative stability of the quasi-one-dimensional (Q1D) pentagon and hexagon ice nanotubes. Electronic structure calculations indicate the two Q1D ice nanotubes have nearly the same band structures and energy bandgap as those of proton-ordered bulk ice Ih. Ab initio molecular-orbital and density-functional theory calculations, as well as three classical potential models of water, are also employed to investigate the relative stability of the pentagon and hexagon water clusters (H2O)30, (H2O)60, and (H2O)120. Clusters of this kind can serve to bridge the gap between the small polygonal water rings and the infinitely long Q1D polygon ice nanotubes. It is found that the polygon water prisms with the size (H2O)120 begin to show the relative energetic behavior of the infinitely long polygon ice nanotubes.