Hello all,

I am trying to apply a set of harmonic distance restraints between pairs of protein atoms in my system, which is protein/ligand/water/ions in a periodic box.

The way i am doing this is to use the bond type 6 and to add these bonds at the end of the [bonds] section in my topology file, after the system has been energy minimised and i have performed position restrained MD, without these harmonic distance restraints.

I can then run it through grompp with no problems and start mdrun. If i only have a few (ie less than about 30) harmonic distance restraints then the simulation if fine and runs happily. However if i increase the number of restraints then mdrun crashes due to lincs warnings and it also says that the are inconsistent shifts, (the number of inconsistent shifts varies depending on which atoms i choose to restrain and also the number of atoms chosen) a warning not seen with less harmonic distance restraints.

I should also say that i have run this system without these harmonic restraints without problems for tens of nanoseconds already. Also this problem can be repeated if i try to use the [distance_restraints] however it requires less restraints to get the inconsistent shift warning (and lincs problems) this way.

If anyone can give me an idea of what is causing this problem it would be warmly appreciated, or even just how to detect which of the harmonic distance restraints will cause the problem before i run mdrun so i can replace the problem 'bonds' in the topology file.

Thanks for any advice you can give

Tom Piggot


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TJ Piggot
[EMAIL PROTECTED]
University of Bristol, UK.
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