$RDF group                     (relevant for RUNTYP=MD)
 
  This group defines the pairs of atoms for which the
radial distribution functions are to be computed, at the
end of a molecular dynamics trajectory.  The input is
similar in style to $EFRAG, consisting of separate lines,
with the word STOP ending each particular pair.
 
Line 1.   NRDF=
gives the number of RDFs which should be computed.
 
Line 2.       
gives a string for the printout (a good choice involves
both atoms, such as ClCl), the name of the $FRAGNAME
containing the first atom of the pair, the name of the
$FRAGNAME input group with the second atom of the pair, and
how many such pairs exist.
 
Line 3.     
gives a label (arbitrary), the position of the atom within
the $FRAG1 group, and the 2nd atom's within the $FRAG2.
This line must be repeated  times.
 
Line 4.    STOP
the word STOP ends this RDF's pair input.
 
Lines 2-4 must then be repeated a total of  times.
 
An example will make this all clear.  If there is only one
type of fragment used, such as water (so $EFRAG contains
only FRAGNAME=WATER), and assuming that this $WATER group
defining the water EFP has atoms in the order O,H,H:
 
$RDF
nrdf=3
OO       water   water    1
  dum   1   1
STOP
OH       water   water    4
  dum   1   2
  dum   1   3
  dum   2   1
  dum   3   1
STOP
HH       water   water    4
  dum   2   2
  dum   2   3
  dum   3   2
  dum   3   3
STOP
 $end