# Single-Site Local-Density Potentials for the Mesoscopic Representation of Water Based on the SAFT-VR Mie Equation of State

## TL;DR

This paper introduces three mesoscopic water models that accurately predict water's physical properties across various temperatures.

## Contribution

The paper introduces new mesoscopic water models based on the SAFT-VR Mie equation of state with local density-dependent potentials.

## Key findings

- All three models accurately predict vapor-liquid equilibrium and isothermal compressibility of water.
- Adding a square-gradient term minimally affects bulk properties but improves interfacial tension predictions.
- The model with an association term performs best across a wide range of conditions.

## Abstract

In this article,
we present three mesoscopic models for water.
All three models make use of local density-dependent interaction potentials,
as employed within the Pagonabarraga-Frenkel framework [PagonabarragaI.; FrenkelD.J. Chem.
Phys.2001, 115, 5015–5026]. The forms of these three
interaction potentials are based on the free energy function of the
SAFT-VR Mie equation of state (EoS) [LafitteT.J. Chem. Phys.2013, 139, 15450424160524
10.1063/1.4819786]. Two of these models represent the water–water
interaction as a spherically symmetric Mie interaction with temperature-dependent
parameters, while the third model works with a temperature-independent
Mie potential and explicitly models the effect of hydrogen bonding
using an association term. All three models provide good predictions
of the vapor–liquid equilibrium of water over a wide temperature
range. They also give accurate predictions of the isothermal compressibility
for both sub- and supercritical conditions. To model the interfacial
tension of the vapor–liquid interface with our mesoscale simulations,
we added a square-gradient term to our potential energy function.
We show that the addition of this term has a minimal effect on the
bulk properties of water. However, by parametrizing the coefficient
of this term as a function of temperature, all three models again
provide excellent predictions of water’s interfacial tension
over a wide temperature range. Of the three models, our preference
is for the model that includes an association term, as this model
can operate successfully over a wider range of conditions.