Difference between revisions of "Nonbonded interactions"
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| + | == The forces == | ||
There are: | There are: | ||
* overlap repulsion a.k.a. exchange force a.k.a. steric repulsion (a.k.a. hard-core,Born) ... (pauli repulsion, degeneracy pressure?) | * 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]]: | And the three components of the [[Van der Waals force]]: | ||
* London dispersion force (mutually induced dipole force), | * London dispersion force (mutually induced dipole force), | ||
* Debye force (dipole - induced dipole force) | * Debye force (dipole - induced dipole force) | ||
* Keesom force (dipole - 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. :<br> | ||
| + | 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.<br> | ||
| + | A rough estimation for pairwise interactions. Corrected parameters are used to get better results. | ||
| + | E.g. for C to H nonbonded interaction forces. | ||
| + | |||
| + | {{wikitodo|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 sp<sup>3</sup> 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) | ||
Revision as of 17:11, 23 August 2018
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)
