cat <<eof > min
  step 1 minimizes wat with protein fixed.
 &cntrl
  imin=1, maxcyc=5000, ncyc=1000, ntb=1, ntr=1, cut=12,
  restraint_wt=500.0,
  restraintmask=':1-318',
 &end
eof
$MPI_HOME/bin/mpirun -np 4 $AMBERHOME/exe/sander.MPI -O -i min \
-c PLP_617_xtal_nolig.crd  -p PLP_617_xtal_nolig.top  -ref PLP_617_xtal_nolig.crd -o step1.out -r step1.rst