# Non-conformal coarse-grained potentials for water

## TL;DR

This paper evaluates coarse-grained water models using ANC and Stockmayer potentials, highlighting their limitations in transferability across different thermodynamic conditions and the need for more complex models.

## Contribution

It introduces a fitting approach for coarse-grained water potentials and analyzes their transferability issues, emphasizing the need for more sophisticated models.

## Key findings

- Symmetrical potentials are non-transferable across state points.
- Adding a point dipole alone does not ensure accuracy or transferability.
- Transferability may require more complex potential models.

## 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 density function and the density 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.