From: Hui-Hsu (Gavin) Tsai [contr] (tsaih_at_ncifcrf.gov)
Date: Mon May 31 2004 - 11:06:04 CDT
  Hi,
    I am trying to run membrane calculations with NPT ensemble.
  The initial membrane structure was generated from the membrane plugin from 
VMD. However, NAMD keeps on giving me these error messages:
****************************************************************
FATAL ERROR: Periodic cell has become too small for original patch grid!
Possible solutions are to restart from a recent checkpoint,
increase margin, or disable useFlexibleCell for liquid simulation.
------------- Processor 11 Exiting: Called CmiAbort ------------
Reason: FATAL ERROR: Periodic cell has become too small for original patch 
grid!
Possible solutions are to restart from a recent checkpoint,
increase margin, or disable useFlexibleCell for liquid simulation.
********************************************************************
 My setup for NPT calculations are as below:
langevin        on
langevinDamping 10
langevinTemp    300.0
# Constant Pressure Control (variable volume)
useGroupPressure      yes ;# needed for rigidBonds
useFlexibleCell       no
useConstantArea       no
langevinPiston        on
langevinPistonTarget  1.01325 ;#  in bar -> 1 atm
langevinPistonPeriod  100.
langevinPistonDecay   50.
langevinPistonTemp    300.0
  Is there anyone who has experience could give me some advice/comments? 
Thanks.
  Gavin
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