For a system of protein containing phenylalanine residue, I used following command to calculate pi-pi interaction
SKIP ALL EXCL vdw Elec
interaction select resname phe .and. type C* end sele resname phe .and. type C* end
ECHO "PHEC PHEC" @X ?VDW ?ELEC
I expected to see at least one of the two terms to be negative. But both VDW and ELEC are positive.