Nonbonded interactions
The forces
There are:
- overlap repulsion a.k.a. exchange force a.k.a. steric repulsion (a.k.a. hard-core,Born) ... (pauli repulsion, degeneracy pressure?)
(repulsive, sort range, exponetial decay, can get very strong)
And the three components of the Van der Waals force:
- London dispersion force (mutually induced dipole force),
- Debye force (dipole - induced dipole force)
- Keesom force (dipole - dipole force)
(attractive,longer range => many atoms can contribute => bigger blocks have smaller equilibrium seperation)
Models
According to Nanosystems 3.3.2.e. :
In computational chemistry it is common that polar interactions are treated separately but overlap repulsion is included
exp-6 potential
As specific example in the MM2 model used is the Buckingham (or exp-6) potential.
A rough estimation for pairwise interactions. Corrected parameters are used to get better results.
E.g. for C to H nonbonded interaction forces.
(wiki-TODO: Add the math of the model & legend.)
Corrections tweaks "hacks"
Atoms in for gem-gum technology relevant materials are strongly bond to other atoms which can more or less significantly shift electron density distributions away from high symmetry.
- Nonbonded interaction between nitrogen oxygen (both sp3 their lone pairs are contacting) (solved by the introduction of lone pair pseudoatoms - ???)
- Covalently surface passivating hydrogen atoms have their electrons move to the passivated surface a bit. (solved by the hack of shifting the position of the atom inward for force calculation - by 0.915 in MM2)
