Abstract
Equilibrium Born-Oppenheimer molecular dynamics simulations have been performed in the canonical ensemble to investigate the structural properties of liquid water and ice Ih (hexagonal ice) at 298 and 273 K, respectively, using a state-of-the-art non-local correlation functional, whilst size effects have been examined explicitly in the case of liquid water. This has led to improved agreement with experiments for pair distribution functions, in addition to molecular dipole moments, vis-a-vis previous flavours of ab-initio molecular dynamics simulation of water, highlighting the importance of appropriate dispersion. Intramolecular geometry has also been examined, in addition to hydrogen-bonding interactions; it was found that an improved description of dispersion via non-local correlation helps to reduce over-structuring associated with the Perdew-Becke-Ernzerhof (PBE) and other commonly-used functionals.
Highlights
IntroductionThe simulation of water [1,2,3,4,5,6,7] and ice [8], or of clathrate hydrates [9], and other condensed matter aqueous systems in the liquid or solid state, using density functional theory-based functionals, can be quite problematic, owing in large part to challenges in modelling dispersion effectively [1,2,3,4,5,6,7,8,9]
We adopt the implementation of van der Waals (vdW)-DF by Román-Pérez and Soler [15], using revPBE exchange in conjunction with non-local vdW correlation [13], termed “DRSLL” following relatively positive initial results in the simulation of liquid water [14], to carry out equilibrium
This increasing closeness of the pressure vis-à-vis ambient pressure upon increasing system size for both ice and liquid water underlines the importance of achieving a “certain” threshold minimum size for the convergence of the pressure tensor
Summary
The simulation of water [1,2,3,4,5,6,7] and ice [8], or of clathrate hydrates [9], and other condensed matter aqueous systems in the liquid or solid state, using density functional theory-based functionals, can be quite problematic, owing in large part to challenges in modelling dispersion effectively [1,2,3,4,5,6,7,8,9]. From the perspective of ab-initio molecular dynamics (AIMD), to achieve qualitatively similar results with experimental structural quantities, such as pairwise radial distribution functions (RDFs) for liquid water, it has been necessary to use temperatures perhaps 20% higher, due to over-structuring by the functionals [1], e.g., Perdew-Becke-Ernzerhof (PBE) [10]. Born-Oppenheimer molecular dynamics (BOMD) in the canonical ensemble of liquid water and ice Ih. Our goal is the study of structural properties of water and ice, with respect to assessing the relative accuracy of DRSLL with respect to experiment. Understanding system size effects on structural and dipolar properties is of relevance to ab initio simulation, in setting the “lower bounds” of what is necessary to capture physically accurate data from
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