Non-conformal coarse-grained potentials for water

Abstract

Water is a notoriously difficult substance to model both accurately and efficiently. Here, we focus on descriptions with a single coarse-grained particle per molecule using the so-called Approximate Non-Conformal (ANC) and generalized Stockmayer potentials as the starting points. They are fitted using the radial distribution function and the liquid-gas density profile of the atomistic SPC/E model by downhill simplex optimization. We compare the results with monatomic water (mW), ELBA, as well as with direct Iterative Boltzmann Inversion (IBI) of SPC/E. The results show that symmetrical potentials result in non-transferable models, that is, they need to be reparametrized for new state-points. This indicates that transferability may require more complex models. Furthermore, the results also show that the addition of a point dipole is not sufficient to make the potentials accurate and transferable to different temperatures (300 K-500 K) and pressures without an appropriate choice of properties as targets during model optimization.

Extended coarse-grained dipole model for polar liquids: Application to bulk and confined water

“…We observe that the confined CG system ,in which a water molecule is coarse-grained into an uncharged spherically symmetric bead (CG-wflj), overestimates the first density peak and exhibits a shoulder peak at about 2 molecular diameter away from the wall compared to the AA SPC/E water model. This clearly shows that the bulk fluid-fluid potential optimized for the single-site CG water is not transferable to the non-bulk (inhomogenous) environment [24]. In other words, the molecular packing of the water molecules close to an interface is quite different than in bulk.…”

“…The double-well-type shape potential has been shown to be important to represent the tetrahedral packing of water [38]. A simple Stockmayer fluid [21] (point dipole + LJ interaction site), which does not have a double-well-type shape potential, may not be able to fully represent the tetrahedral packing of the water molecules [24]. Therefore, it is essential to have a double-well shape potential between the dipoles in order to reproduce the water structure.…”

“…A soft sticky dipole potential is also developed for liquid water, which is the same as the BBL model, except that the hard-sphere interaction is replaced by the softer Lennard-Jones potential [16]. More generally, the generalized Stockmayer (GSM) potential is developed for polar liquids that consists of a spherical Kernel with dipole-dipole interaction [23] and has been recently applied for water [24]. There are also efforts to match properties of water to experiments (top-down CG methods).…”

Self-Assembly of Phosphocholine Derivatives Using the ELBA Coarse-Grained Model: Micelles, Bicelles, and Reverse Micelles

“…On the other hand, transferability and accuracy remain concerns as with other water models. 72 Recent reviews of water models are provided by Darréet al 73 and Onfriev and Izadi. 74 Here we assess the quality of this force field to study dodecylphosphocholine (DPC) micelle, bicelles with DPPC and 1,2-dihexaoyl-sn-glycero-3-phosphocholine (DHPC), and reverse micelles of DPPC/cyclohexane/water.…”

Improved general-purpose five-point model for water: TIP5P/2018

“…8 Even non-conformal models that do not obey the energy and distance scaling in a Lennard-Jones manner have been introduced. 9,10 Given the number of models, it is perhaps somewhat surprising that most modern two-body interaction water models are based on the functional form of the 1933 model of Bernal and Fowler, 11 that is, the energy of two interacting water molecules is given as…”