The term E elec ik describes electrostatic interactions between atoms i and k from atom-centered multipoles up to hexadecapole on all atoms, which were derived from a distributed multipole analysis of the B3LYP/6-311G** charge density . Charge-charge, charge-dipole and dipole-dipole interactions were calculated with Ewald summation. All other interactions were calculated between whole molecules with a centre of mass distance less than 25Å.