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Van der Waals interactions (Read 1564 times)
Gerrit-Jan Linker
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Van der Waals interactions
27.05.10 at 08:33:17
 
Van der Waals interactions
 
The van der Waals forces are the attractive or repulsive forces between molecules (or between parts of the same molecule) other than those due to covalent bonds or to the electrostatic interaction of ions with one another or with neutral molecules.  
 
v/d Waals interactions are also called London interactions or dispersion interactions.
 
The term includes:
 
  * force between permanent dipole and a corresponding induced dipole
  * instantaneous induced dipole-dipole forces (London dispersion force).
 
It is also sometimes used loosely as a synonym for the totality of intermolecular forces.
 
The van der Waals forces are modelled using the Lennard-Jones potential:
VLJ= 4ε [(σ/r)12 - (σ/r)6]
ε is the depth of the potential well
σ is the finite distance at which the inter-particle potential is zero
r is the distance between the particles
 
Actually only the r-6 term is modeling the dispersion force. The r-12 term is there to provide the steep repulsion needed at short distance. It has nothing to do with dispersion.
 
See also:
Dispersion
http://www.oraxcel.com/cgi-bin/yabb2/YaBB.pl?num=1216672162
Lennard Jones potential
http://en.wikipedia.org/wiki/Lennard-Jones_potential
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« Last Edit: 16.12.12 at 16:27:40 by Gerrit-Jan Linker »  

Gerrit-Jan Linker
Linker IT Software
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