Difference between revisions of "Nonbonded interactions"
(→The forces: more readable formatting) |
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* Keesom force (dipole - dipole force) | * Keesom force (dipole - dipole force) | ||
(attractive,longer range => many atoms can contribute => bigger blocks have smaller equilibrium seperation) | (attractive,longer range => many atoms can contribute => bigger blocks have smaller equilibrium seperation) | ||
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| + | Nanosystems: The term "Van der Waals forces" is usually used for the attractive components alone by physicists.<br> | ||
| + | {{wikitodo|The wikipedia page about [[superlubricity]] (here: [https://en.wikipedia.org/wiki/Superlubricity] 2018-08) mentiones repulsive VdW forces (negative Hamaker constant). Find out if that is just due to a mix-in of overlap repulsion (likely?) or a genuine effect?}} | ||
== Models == | == Models == | ||
Revision as of 17:24, 23 August 2018
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)
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)
Nanosystems: The term "Van der Waals forces" is usually used for the attractive components alone by physicists.
(wiki-TODO: The wikipedia page about superlubricity (here: [1] 2018-08) mentiones repulsive VdW forces (negative Hamaker constant). Find out if that is just due to a mix-in of overlap repulsion (likely?) or a genuine effect?)
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)
