The CFF belongs to the group of methods called molecular mechanics where the potential energy of a molecule, a molecular complex or a crystal is calculated as a sum of inter-atomic potentials, whose parameters are ideally obtained by optimization on experimental structural and spectroscopic data for the pure substances. A set of parameters is called a force field.
It is a tool with which you can develop force fields, in the sense that you can optimize the parameters of potential energy functions on several categories of data for molecules in gaseous and crystalline states.
The imbedded methods allow for calculation of molecular properties such as conformations, vibrational frequencies and thermodynamic functions. The integrated optimisation facility is unique and fundamental to the CFF concept.
The most important technical contributions from the Danish group are: weighted Levenberg-Marquardt optimization, a crystal simulator using Ewald sums and an interactive graphical interface to the optimization algorithm GOPT (Graphics OPtimization Tool).
The uniqueness of CFF is found in its optimization capabilities. At present CFF can optimize on bond lengths, valence angles, torsional angles, out-of-plane angles, non-bonded distances, unit cell dimensions, lattice energies, molecular potential energies, dipole moments, and vibrational frequencies.
Force fields based on theoretical data obtained from large-scale ab initio calculations at the MP2 level or employing DFT to include electron correlation are currently being optimised.