High-Order Ab Initio Valence Force Field with Chemical Pattern-Based Parameter Assignment

Bonded interactions are fundamental ingredients of molecular mechanics force fields because they directly determine the local structure of a molecule. In this work, we parametrize the advanced bonded energy functionals that consider the vibrational anharmonicity, the coupling effects, and the out-of-plane bending for sp2-hybridized atoms. It is expected that these models can describe the spectroscopic properties and overall structures of a molecule more accurately when they are used with polarizable AMOEBA-based force fields. Bonded (or valence) interactions, which directly determine the local structures of the molecules, are fundamental parts of molecular mechanics force fields (FFs). Most popular classical FFs adopt the simple harmonic models for bond stretching and angle bending and ignore cross-coupling effects among the valence terms. This may lead to less accurate vibrational properties and configurations in molecular dynamics (MD) simulations. AMOEBA models utilize an MM3(MM4)-style bonded interaction model, in which the vibrational anharmonicity, the coupling effects among different energy terms, and the out-of-plane bending for sp2-hybridized atoms are considered. In this work, we report the development of bonded interaction parameters for a wide range of chemistry based on quantum mechanics (QM). About 270 atomic types defined by SMARTS strings were used to model the valence interactions. Our results indicate that the resulting valence parameters produce accurate vibrational frequencies (RMSD from QM is less than similar to 36.6cm(-1)) over a large set of molecules with diverse functional groups (445 molecules). By contrast, the harmonic models usually give an RMS error greater than 60cm(-1). Meanwhile, this model accurately reflects the potential energy surface of the out-of-plane bending. Our model can generally be applied to the AMOEBA family and any MM3(MM4)-based molecular mechanics FFs.

Automated summary

This study develops quantum mechanics-based chemical bond interaction parameters, taking into account vibrational anharmonicity, coupling effects, and out-of-plane bending of hybridized atoms. The results show that this model accurately describes the vibrational properties and structures of molecules, and is more accurate than traditional harmonic models.