abcd;0 may be assigned from parameter libraries based on the chemical environment, or they may be specifically fitted (i.e. bespoke) for an individual torsion angle of a specific molecule. The non-covalent interaction between the terminal atoms of the torsion angle may also be modeled using pairwise Coulomb and Lennard-Jones interactions on atoms separated by exactly three bonds (i.e. "1-4 interactions"), which may be modified from conventional non-bonded terms using scaling factors or alternative parameter values. Because the 1-4 distance depends strongly (but not exclusively) on the torsion angle, it may be considered as another contribution to the torsional potential energy. because the total energy includes contributions from the quantum nature of covalent bonding such as resonance and conjugation, as well as non-covalent interactions such as electrostatic and steric effects on vicinal functional groups. As the torsion angle is varied in a molecule, several important properties of the molecule are affected including the electronic character of the central bond as well as steric and other nonbonded interactions between groups on opposite sides of the bond. Importantly, the torsion angle dependence of these properties can induce relaxations in the orthogonal degrees of freedom as the torsion angle is varied.