Nonbonded interactions

The forces

The repulsive forces:

• 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)

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The attractive forces: (The Van der Waals force which split up into three):

• 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)