Pair interaction energies: TCL error -reg

From: Jeyaram R A (ra.jeyaram_at_vit.ac.in)
Date: Thu Feb 08 2018 - 01:32:44 CST

Dear NAMD users,

I want to calculate pair interaction energy by using amber generated parameters and coordinates, while executing the script it shows the following error.

script:

# pair interaction energy calculation
# Amber generated top and crd file is used
amber yes # Specify this is AMBER force field
# amber generated top and crd file
parmfile 1.top # Input PARM file
coordinates 1.crd # Input coordinate file
structure md.nc

# approximations
timestep 2.0
cutoff 8.0
switchdist 7.0
pairlistdist 10.0
exclude scaled1-4
1-4scaling 0.83333 # 1/scee where scee in amber is 1.2
# Atoms in group 1 have a 1 in the B column; group 2 has a 2.
pairInteraction on
pairInteractionFile pair.pdb
pairInteractionCol B
pairInteractionGroup1 1
pairInteractionGroup2 2

# First frame saved was frame 500.
set ts 500

coordinates open NetCDF md.nc

# Read all frames until nonzero is returned.
while { ![coordinates read] } {
  firstTimestep $ts
  run 0
  incr ts 500
}
coordinates close

error:

Reason: FATAL ERROR: can't use empty string as operand of "!"
    while executing
"while { ![coordinates read] } {
  firstTimestep $ts
  run 0
  incr ts 500
}"
    (file "pair.inp" line 29)

Charm++ fatal error:
FATAL ERROR: can't use empty string as operand of "!"
    while executing
"while { ![coordinates read] } {
  firstTimestep $ts
  run 0
  incr ts 500
}"
    (file "pair.inp" line 29)

Aborted (core dumped)

                                                                     Thanks in advance

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