[gmx-developers] Re: Pull code and virial

[Berk Hess]

Justin MacCallum wrote:

>> I guess the best way to fix this would be to calculate the pull virial
>> (also for constraint pulling)
>> in the pull code, store it in the forcerec and add it in calc_virial,
>> just as is done
>> for the grid part of the electrostatics virial.
>
>
> That sounds very reasonable to me. I'll leave it to you though as I am 
> not at all familiar with code that does the virial calculations in 
> GROMACS.

I have implemented the virial correction for afm and umbrella pulling.
But I have noticed that the afm and umbrella pull code is not correct.
The forces are only applied to the 'other' groups, not to the reference 
group.
So the system is no longer Newtonian and one can not check things
such as energy conservation.

When there is no absolute reference I have now also added minus the force
to the reference group and now we have energy conservation and zero average
virial for pulling on two atoms with charge.

I would consider this force problem a pretty serious error.
I don't know how others think about it.

If there are no objections, I will commit tomorrow.

Berk.