Four-body singlet potential energy surface for reactions of calcium monofluoride

A full six-dimensional Born-Oppenheimer singlet potential energy surface is constructed for the reaction CaF + CaF $\to$ CaF${}_2$ + Ca using a multireference configuration interaction (MRCI) electronic structure calculation. The {\it ab initio} data thus calculated are interpolated by Gaussian process (GP) regression. The four-body potential energy surface features one $D_{2h}$ global minimum and one $C_s$ local minimum, connected by a barrierless transition state that lends insight to the reaction mechanism. This surface is intended to be of use in understanding ultracold chemistry of CaF molecules.