Constraint failure; simulation has become unstable

From: Wendy González (
Date: Fri Jan 07 2011 - 14:42:46 CST

Dear NAMD Users,

I am working with 3 systems, the only difference between them are:

a) 2 histidines protonated
b) 1 histidine protonated, the second is neutral
c) Both histidines neutral

I run several nanoseconds of simulations on this systems and they did not
have problems. I applied the reloadCharges command (increasing the charge of
the same glutamate in the 3 systems) and the results are:

a) Run normally
b) ERROR: Constraint failure in RATTLE algorithm for atom XXXX ERROR:
Constraint failure; simulation has become unstable.
c) Run normally

In case b) I said "atom XXXX", because I run 3 different simulations and the
error is with a different atom each time.

Any suggestion??? What could be happening???

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