In the above equation, R vdw i represents the atom-in-molecule van der Waals radius for atom i which is obtained from the atom-in-molecule static polarizability α i (0), the free-atom static polarizability α 0 i (0) and the free-atom van der Waals radius R 0,vdw i , the latter defined for noble gases as half of the distance between two atoms where exchange-repulsion balances London's dispersion attraction.