On the <scp>many‐body</scp> nature of intramolecular forces in <scp>FFLUX</scp> and its implications
Anton Konovalov, Benjamin C. B. Symons, Paul L. A. Popelier
Abstract
Abstract FFLUX is a biomolecular force field under construction, based on Quantum Chemical Topology (QCT) and machine learning (kriging), with a minimalistic and physically motivated design. A detailed analysis of the forces within the kriging models as treated in FFLUX is presented, taking as a test example a liquid water model. The energies of topological atoms are modeled as 3 N atoms ‐6 dimensional potential energy surfaces, using atomic local frames to represent the internal degrees of freedom. As a result, the forces within the kriging models in FFLUX are inherently N‐body in nature where N refers to N atoms . This provides a fuller picture that is closer to a true quantum mechanical representation of interactions between atoms. The presented computational example quantitatively showcases the non‐negligible (as much as 9%) three‐body nature of bonded forces and angular forces in a water molecule. We discuss the practical impact on the pressure calculation with N‐body forces and periodic boundary conditions (PBC) in molecular dynamics, as opposed to classical force fields with two‐body forces. The equivalence between the PBC‐related correction terms in the general virial equation is shown mathematically.