HIPPO (Hydrogen-like Intermolecular Polarizable POtential) is an advanced polarizable force field at the intersection of ab initio and empirical potentials. It starts with a model representing each atom by a core point charge and a diffuse hydrogen-like, anisotropic electron density. We use this density-based model to derive classical equivalents of the four intermolecular energy terms of Symmetry Adapted Perturbation Theory (SAPT): electrostatics, induction, dispersion, and exchange-repulsion. The HIPPO formalism has been used to parameterize water, ions, and small organic molecules with great accuracy.<br/><br/>Building upon the existing HIPPO water model, we expand support to a wide range of organic molecules. Results are presented for benzene as a prototypical example. HIPPO successfully reproduced quantum mechanics and experimental results for benzene in the gas, liquid, and solid phase. The inclusion of charge penetration accurately describes the electrostatic interactions in aromatic systems. For example, the benzene crystal structure is better reproduced by HIPPO than by our previous AMOEBA force field.<br/><br/>We detail HIPPO parameter fitting and validation across a varied database of 160 small organic molecules. Quantum mechanical calculations, including SAPT results for dimers, are coupled with molecular dynamics simulation of thermodynamic and transport properties. The parameter optimization process begins by fitting dimer energy components to their SAPT counterparts for systems in the S101x7 database. Water is used as a probe for other molecules via SAPT computations for molecule-water systems in different configurations. In addition, the Virtual Chemistry database provides liquid properties, such as enthalpy of vaporization, density, and dielectric constant for our target dataset. A genetic search over parameter space coupled with automated least-squares refinement provides a consistent, optimal HIPPO model. The completion of the organic molecule model lays the groundwork for developing a HIPPO force field for proteins and eventually other biomolecule classes.

Progress toward the quantum mechanically-based HIPPO force field

Fall 2022 abstracts, posters, and presentations will launch in mid-September.

ACS Fall 2022

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.