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| Pair interactions similar to the typical intermolecular potentials are frequently | | Pair interactions similar to the typical intermolecular potentials are frequently |
| used (e.g. [[Lennard-Jones]] potentials) | | used (e.g. [[Lennard-Jones model|Lennard-Jones]] potentials) |
Revision as of 13:26, 19 March 2007
Modelling of internal degrees of freedom, usual techniques:
Bond distances
Atoms linked by a chemical bond (stretching):
However, this internal coordinates are very often kept constrained (fixed bond distances)
Bond Angles
Bond sequence: 1-2-3:
Bond Angle:
Two typical forms are used to model the bending potential:
Dihedral angles. Internal Rotation
Bond sequence: 1-2-3-4
Dihedral angle () definition:
Consider the following vectors:
- ; Unit vector in the direction of the 2-3 bond
- ; normalized component of ortogonal to
- ; normalized component of ortogonal to
For molecules with internal rotation degrees of freedom (e.g. n-alkanes), a torsional potential is
usually modelled as:
or
Van der Waals intramolecular interactions
For pairs of atoms (or sites) which are separated by a certain number of chemical bonds:
Pair interactions similar to the typical intermolecular potentials are frequently
used (e.g. Lennard-Jones potentials)