[gmx-users] TOP file question

[Peter Eastman]

After further study of the documentation, I find myself getting more confused rather than less.  I see that the [pairs] and [pairtypes] directives only specify LJ parameters, not Coulomb parameters.  (There's a function type 2 for [pairs] that does include charges, but the manual says that function type is only used for free energy calculations.)  How do I select the latter when gen-pairs is off?  Is it simply assumed that 1-4 Coulomb interactions are never reduced for force fields that don't use gen-pairs?  Table 5.5 lists an alternate directive, [pairs_nb] that does specify Coulomb parameters as well as LJ.  But no other mention of this directive appears anywhere else in the manual, there doesn't seem to be any corresponding [pairtypes] option, and a grep reveals that "pairs_nb" never occurs in any file in the entire top directory.

What am I misunderstanding?

Peter