PIV ...
LABEL=c1
PRECISION=1000000
VOLUME=25.1264   
NLIST
ONLYCROSS
REF_FILE=Liq.pdb
PIVATOMS=2
ATOMTYPES=OW1,HW
SFACTOR=1.
SORT=1  
SWITCH1={RATIONAL R_0=0.5 MM=12 NN=4}
NL_CUTOFF=3.
NL_STRIDE=1
NL_SKIN=0.1
... PIV
PIV ...
LABEL=c2
PRECISION=1000000
VOLUME=25.1264   
NLIST
ONLYCROSS
REF_FILE=Ice.pdb
PIVATOMS=2
ATOMTYPES=OW1,HW
SFACTOR=1.
SORT=1  
SWITCH1={RATIONAL R_0=0.5 MM=12 NN=4}
NL_CUTOFF=3.
NL_STRIDE=1
NL_SKIN=0.1
... PIV

PRINT ARG=c1,c2 STRIDE=1  FILE=colvar FMT=%15.2f

