$FRGRPL group
 
This group defines the inter-fragment repulsive potential
for EFP1 potentials.  It accounts primarily for exchange
repulsions, but also includes charge transfer.  Note that
the functional form used for the fragment-fragment
repulsion differs from that used for the ab initio-fragment
repulsion, which is defined in the $FRAGNAME input.  The
form of the potential is
       N
      sum   A * exp[-B * r]
       i     i        i
 
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-1-  PAIR=FRAG1 FRAG2
 
specifies which two fragment repulsions are being defined.
$FRAGNAME input for the two names FRAG1 and FRAG2 must have
been given.
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-2-  NAME1 NAME2 A B
            *or*
     NAME1 NAME2 'EQ' NAME3 NAME4
 
NAME1 must be one of the "NAME" points defined in the
$FRAG1 group's REPULSION POTENTIAL section.  Similarly
NAME2 must be a point from the $FRAG2 group.  In addition,
NAME1 or NAME2 could be the keyword CENTER, indicating the
center of mass of the fragment.
 
A and B are the parameters of the fitted repulsive
potential.
 
The second form of the input allows equal potential fits to
be used.  The syntax implies that the potential between the
points NAME1 and NAME2 should be taken the same as the
potential previously given in this group for the pair of
points NAME3 and NAME4.
 
If there are NPT1 points in FRAG1, and NPT2 points in
FRAG2, input line -2- should be repeated NPT1*NPT2 times.
Terminate the pairs of potentials with a "STOP" card.
Any pairs which you omit will be set to zero interaction.
 
Typically the number of points on which fitted potentials
might be taken to be all the nuclei in a fragment, plus
the center of mass.
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Repeat lines -1- and -2- for all pairs of fragments, then
terminate the group with a $END line.