[gmx-developers] Large VCM(group rest): Temp-cm: inf

[Berk Hess]

Hi,

I have added a check on group_ndf.

But how can you have a vcm group with non-zero mass, but with zero 
degrees of freedom?

Berk

Carsten Kutzner wrote:
> Hi,
>
> we appear to have another small problem with the CVS version.
> For a protein in water system, where comm-grps=Protein is
> chosen we continuously get the following line outputted to log:
>
> Large VCM(group rest):      0.00005,     -0.00002,     -0.00004, 
> Temp-cm:          inf
> Large VCM(group rest):      0.00006,     -0.00003,     -0.00004, 
> Temp-cm:          inf
> Large VCM(group rest):      0.00006,     -0.00003,     -0.00003, 
> Temp-cm:          inf
> Large VCM(group rest):      0.00006,     -0.00004,     -0.00002, 
> Temp-cm:          inf
> Large VCM(group rest):      0.00006,     -0.00005,     -0.00001, 
> Temp-cm:          inf
> ...
>
> This happens also for the non-MPI mdrun. The problem is that in 
> check_cm_grp (vcm.c)
> the number of degrees of freedom for the 2nd group are zero. Thus
>
> Temp_cm = 2*ekcm/vcm->group_ndf[g];
>
> becomes infinity, triggering the message. This is just an output 
> problem, since
> nothing needs to be done to the COM of the second group anyway. 
> However, the md.log files
> become HUGE when this is outputted at every step.
>
> Carsten
>
>
>
>