[gmx-users] how does gromacs handle the force on the virtual site of the TIP4P model

[Mark Abraham]

On 10/02/2012 5:11 AM, GZ Zhang wrote:
> Hi, ALL
>
>     We are writing our own MD program to simulate water and the TIP4P 
> model is being considered.
> I am wondering that how does GROMACS program handle the force on the 
> massless M site of the TIP4P
> model? It would be better to be informed the algorithm(or the code in 
> GROMACS). Thanks.

It's a virtual site. The forces get projected onto the real sites from 
which it is constructed. See manual section 4.7

Mark