Non-bonded interactionsΒΆ
The inter-molecular or nonbonded interactions consist of energy components interact between pairs of atoms and depend only on the interatomic distances.
Nonbonded interactions consist of several energy components as follows:
- Electrostatic (Coulombic) interactions. This arises due to charges on atoms and they are considered long-range in nature.
- Dispersive (van der Waals) interactions. Such interactions are due to electron cloud fluctuations, forming instanteneous dipoles. They can be found even in inert gas systems and neutral atoms.
- Urey-Bradley (UB) 1-3 atom pair interactions - This is specific to CHARMM FF schemes. They correlate with the angle interactions. Diagram below shows the UB interactions for the benzene molecule.
- Others. This includes dipole-dipole interactions such as the hydrogen bonds, charge-dipole interactions, etc. However, most FF schemes do not explicitly include such interactions as they are implicitly included in the above mentioned interactions.
Note
For covalent molecules nonbonded interactions do not apply to 1-2 and 1-3 bonded atoms, except the UB interactions. For the 1-4 atoms, a constant scaling factor is usually applied, depending on the FF schemes.