general force field (GFF)

https://doi.org/10.1351/goldbook.G02611
A force field expressed in terms of \(3\ N-6\) basis coordinates: \[V=\frac{1}{2}\, \sum f_{ij}\ S_{i}\ S_{j}\] \[V=\frac{1}{2}\, \sum F_{ij}\ S_{i}\ S_{j}\] where \(f_{ij}\) (or \(F_{ij}\)) are @[email protected] and the basis coordinates \(S\) (or sometimes \(s\)) may be internal symmetry coordinates, local symmetry coordinates or any others suitable to the problem, but the number of the coordinates has to be reduced to \(3\, N-6\) (\(3\, N-5\) for linear molecules), \(N\) being the number of atoms in the molecule.
Source:
PAC, 1978, 50, 1707. (Definition and Symbolism of Molecular Force Constants) on page 1709 [Terms] [Paper]