igroup {<igroup-statement>} end
<igroup-statement> :==
interaction <atom-selection> <atom-selection>
[weight { <energy-term> <real> } end]
Compute interaction terms between the specified sets of atoms
during all energy calculations:
- for pairwise interactions (i-j) i in a and j in b
- for angles (i-j-k), i,j,k have to be in a or b with at least
one component in a and at least one in b.
- for dihedrals & impropers (i-j-k-l), i,j,k,l have to be in a or b
with at least one component in a and at least one in b.
Each energy term can be weighted by a weighting factor.