A study on the properties and transferability of force fields in redundant and independent coordinates

The theory of canonical and regular force fields has been used to develop a new approach to study the transferability of force constants in terms of redundant rectilinear internal coordinates. It has been found that the force field of a group of atoms is transferable when it is expressed in canonical form, and that the force field in terms of symmetry-independent coordinates is transferable when these coordinates are orthogonal to the redundancy conditions. As an illustrative example, the approach has been applied to obtain transferable harmonic force constants for the CH 3 group in methane and chloromethane molecules.