Analytical fittings for the global potential energy surface of the ground state of methylene

The fitting strategies do not have any consideration about symmetry factors and provides a full description of continuity over the entire region, from the ground state of CH₂ to the ground states of three separate atoms. From ab initio results, the bond lengths can be divided into three approximate ranges: near the equilibrium bond length, medium range, and very long distance from the equilibrium. Thus, there were six combinations considering the relative energy with respect to the bond angle. Each region have its own properties.