[gmx-users] TIP4P water

[Anton Feenstra]

David van der Spoel wrote:

> On Thu, 18 Dec 2003, Bing Kim wrote:
> 
> 
>>Thanks, guys.
>>
>>I read the manual. It explain that clearly.
>>According to manual, tip4p looks related to "3fd" out of 6 models.
>>But can I think tip4p as "3" if I constrain the geometry of tip4p (rigid).
>>Sorry for bothering you.
>>
> 
> 
> forces go to all atoms, as the M site is a linear combination of the 
> positions of the other atoms, force will be distribbuted in the same way.
> Since a three atom molecule is always planar, the simple linear 
> combination is enough.

Depends if there is freedom in the molecule. YOu probably want the 'm' at
at fixed distance, in stead of the distance depending on the H-O-H angle.
Thus, the use of the '3fd' (three atoms, fixed distance) dummy atom
construction which is not quite a linear combination since it normalizes
the construction to a fixed distance. In any case, forces are re-distributed
according to the position construction (and, believe me, it wasn't easy to
get that implemented correctly!).


-- 
Groetjes,

Anton
  _____________ _______________________________________________________
|             |                                                       |
|  _   _  ___,| K. Anton Feenstra                                     |
| / \ / \'| | | Dept. of Pharmacochem. - Vrije Universiteit Amsterdam |
|(   |   )| | | De Boelelaan 1083 - 1081 HV Amsterdam - Netherlands   |
| \_/ \_/ | | | Tel: +31 20 44 47608 - Fax: +31 20 44 47610           |
|             | Feenstra at chem.vu.nl - www.chem.vu.nl/~feenstra/       |
|             | "If You See Me Getting High, Knock Me Down"           |
|             | (Red Hot Chili Peppers)                               |
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