Long-range intermolecular forces, importance

The fundamental importance of bonding energies between bodies are traditionally divided into two broad classes chemical bond (short-range force), and physical or intermolecular bond (long-range force). The energies are largely dependent on the distance at which one body feels the presence of the other. Usually, they are called a Lennard-Jones potential [34] which has a minimum value at a certain distance. 

If one of the molecules is in a degenerate state, or if they are identical and one is in an excited state, then there will be resonance interactions, which are long range. This intermolecular force may cause the dimer in which one molecule is excited (an excimer) to be much more strongly bound than when both are in the ground state. Resonance is important in excited states of molecular crystals. ... 

Furthermore, the actual Coulomb forces are also important. If the molecules have polar substituents or a permanent dipole moment, or if they are electrically charged in a heteropolar fashion, i.e. the crystals are salts, then the intermolecular interactions are naturally also determined by the static monopole, dipole, and Coulomb forces with their long range. This of course also influences the crystal structures... 

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