AMBER Archive (2008)

Subject: AMBER: vlimit exceeded error

From: priya priya (
Date: Wed Jan 23 2008 - 05:27:37 CST

Hi All

I am doing simulations at 550K using some constraints on the peptide.There is an error read as:

vlimit exceeded for step 64; vmax = 20.6735
vlimit exceeded for step 65; vmax = 26.7190
vlimit exceeded for step 66; vmax = 24.7766
vlimit exceeded for step 71; vmax = 60.0784

     Coordinate resetting (SHAKE) cannot be accomplished,
     deviation is too large
     NITER, NIT, LL, I and J are : 0 1 515 1062 1064
     Note: This is usually a symptom of some deeper
     problem with the energetics of the system.

I have minimized the structure and have equilibrated the system before doing production MD, so i am not able to fine out what is the error. In terms of energy i found that it is showing a sharp increase. could anybody suggest me what is the error.
My input file is a s follows:

imin=0, irest=1, ntx=5,
  nstlim=10000, dt=0.002,gbsa =1,surften=0.005,
  ntc=2, ntf=2,nscm= 1000,
  tempi=492.17, temp0=492.17,
  ntpr=100, ntwe = 300,ntwx=100, ntwr = 300,
  ntb=0, igb=1,

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