Chemisorption of manganese phthalocyanine on Cu(001) surface promoted by van der Waals interactions

van der Waals (vdW) interactions within density functional theory are shown to strongly reduce the distance between manganese phthalocyanine (MnPc) and a Cu(001) surface to that found by x-ray standing wave experiments. Thus, the physisorbed ground state that is predicted within the generalized-gradient approximation formalism is replaced by a chemisorbed ground state once vdW interactions are taken into account. These findings indicate how to systematically obtain the correct theoretical adsorption distance for complex molecules and thus accurately predict the properties of the ensuing molecule/metal interface. The reduction of the experimental work function upon molecular adsorption is satisfactorily accounted for and explained in terms of Friedel-like oscillations of the charge density at the vicinity of the MnPc molecule that change the sign of the charge transfer electric dipole. This shows how vdW interactions can strongly impact charge injection in organic electronic devices. DOI: 10.1103/PhysRevB.87.15541