From: Peter Freddolino (petefred_at_ks.uiuc.edu)
Date: Mon Mar 02 2009 - 10:29:32 CST
are you placing any additional constraints or restraints on the system?
If you visually inspect your structure (maybe comparing the same
structure generated using your new and old procedures), does everything
look ok? Did you get any warnings from psfgen? It's odd that you'd have
difficulties with structures made by psfgen if the initial coordinates
Brittany Morgan wrote:
> Hello all,
> I am having a problem with convergence of the minimization routine. The
> gradient tolerance convergences rapidly at first, but then fluctuates
> around 40-100 and will not continue to decrease. If I try to go ahead
> and run dynamics, even with a very conservative time step (0.5fs with a
> 1e-6 SHAKE tolerance), I get a RATTLE constraint error, but it is not
> the same atom every time.
> I have tried SHAKE on or off during minimization, varying the length of
> minimization from 1,000 to 20,000 steps and I also tried using the
> velocity quenching algorithm for 1,000 steps initially and then doing
> additional conjugate gradient minimization. Turning SHAKE off during
> minimization helped some (fluctuates between 10-40) for one structure at
> least, but it didn’t solve the problem.
> I have never had this problem in the past, and now it is happening for 4
> structures. The difference is that I am using psfgen (using a script,
> not the GUI) to generate the input files for NAMD instead of using
> CHARMM. I can’t find any difference when comparing the output of psfgen
> with the original PDB files, and the structure after minimization is not
> very different from the starting state. I’d prefer not to go back to
> using CHARMM, since it is a pain comparatively for me, but I don’t know
> what else to try.
> Any suggestions?
> Brittany Morgan
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