[gmx-users] TIP4P water
feenstra at chem.vu.nl
Mon Dec 22 09:02:07 CET 2003
David van der Spoel wrote:
> On Thu, 18 Dec 2003, Bing Kim wrote:
>>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!).
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| _ _ ___,| K. Anton Feenstra |
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