Application of quantum chemical topology force field FFLUX to condensed matter simulations: liquid water

We present here the first application of the quantum chemical topology force field FFLUX to condensed matter simulations. FFLUX offers many‐body potential energy surfaces learnt exclusively from ab initio data using Gaussian process regression. FFLUX also includes high‐rank, polarisable multipole moments (up to quadrupole moments in this work) that are learnt from the same ab initio calculations as the potential energy surfaces. Many‐body effects (where a body is an atom) and polarisation are captured by the machine learning models. The choice to use machine learning in this way allows the force field’s representation of reality to be improved (e.g. by including higher order many‐body effects) with no detriment to the computational scaling of the code. In this manner, FFLUX is inherently future‐proof. The “plug and play" nature of the machine learning models also ensures that FFLUX can be applied to any system of interest, not just liquid water. In this work we study liquid water across a range of temperatures and compare the predicted bulk properties to experiment as well as other state‐of‐the‐art force fields AMOEBA(+CF), HIPPO, MB‐Pol and SIBFA21. We find that FFLUX finds a place amongst these.