## 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 @F02481@ 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]