[gmx-users] Force equations of virtual site type 4fdn

Mark Abraham Mark.Abraham at anu.edu.au
Tue Nov 22 10:29:06 CET 2011

On 22/11/2011 7:27 PM, xuji wrote:
> Hi all-gmxers
> The force equations of old virtual site type 4fd were shown in GROMACS 
> manual.
> But the ones of corresponding new type 4fdn are not shown in new 
> GROMACS manual.
> Can someone do me a favor to give the force equations?

You will have seen that the manual also says:

The force
on particles i, j, k and l due to the force on the virtual site are 
computed through chain rule
derivatives of the construction expression. This is exact and conserves 
energy, but it does
lead to relatively lengthy expressions that we do not include here (over 
200 floating-point
operations). The interested reader can look at the source code in vsite.c.

Perhaps you should try this.

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