title: Non-additivity of molecule-surface van der Waals potentials from force measurements.
abstract: Van der Waals (vdW) forces act ubiquitously in condensed matter. Despite being weak on an atomic level, they substantially influence molecular and biological systems due to their long range and system-size scaling. The difficulty to isolate and measure vdW forces on a single-molecule level causes our present understanding to be strongly theory based. Here we show measurements of the attractive potential between differently sized organic molecules and a metal surface using an atomic force microscope. Our choice of molecules and the large molecule-surface separation cause this attraction to be purely of vdW type. The experiment allows testing the asymptotic vdW force law and its validity range. We find a superlinear growth of the vdW attraction with molecular size, originating from the increased deconfinement of electrons in the molecules. Because such non-additive vdW contributions are not accounted for in most first-principles or empirical calculations, we suggest further development in that direction.
authors.affiliation: 1] Peter Grünberg Institut (PGI-3), Forschungszentrum Jülich, 52425 Jülich, Germany [2] Jülich Aachen Research Alliance (JARA)-Fundamentals of Future Information Technology, 52425 Jülich, Germany.
authors.forename: Christian
authors.initials: C
authors.lastname: Wagner
authors.affiliation: 1] Peter Grünberg Institut (PGI-3), Forschungszentrum Jülich, 52425 Jülich, Germany [2] Jülich Aachen Research Alliance (JARA)-Fundamentals of Future Information Technology, 52425 Jülich, Germany.
authors.forename: Norman
authors.initials: N
authors.lastname: Fournier
authors.affiliation: Fritz-Haber-Institut der Max-Planck-Gesellschaft, Faradayweg 4-6, 14195 Berlin, Germany.
authors.forename: Victor G
authors.initials: VG
authors.lastname: Ruiz
authors.affiliation: Max-Planck-Institut für Polymerforschung, Ackermannweg 10, 55128 Mainz, Germany.
authors.forename: Chen
authors.initials: C
authors.lastname: Li
authors.affiliation: Max-Planck-Institut für Polymerforschung, Ackermannweg 10, 55128 Mainz, Germany.
authors.forename: Klaus
authors.initials: K
authors.lastname: Müllen
authors.affiliation: Institut für Festkörpertheorie der Universität Münster, Wilhelm-Klemm-Straße 10, 48149 Münster, Germany.
authors.forename: Michael
authors.initials: M
authors.lastname: Rohlfing
authors.affiliation: Fritz-Haber-Institut der Max-Planck-Gesellschaft, Faradayweg 4-6, 14195 Berlin, Germany.
authors.forename: Alexandre
authors.initials: A
authors.lastname: Tkatchenko
authors.affiliation: 1] Peter Grünberg Institut (PGI-3), Forschungszentrum Jülich, 52425 Jülich, Germany [2] Jülich Aachen Research Alliance (JARA)-Fundamentals of Future Information Technology, 52425 Jülich, Germany.
authors.forename: Ruslan
authors.initials: R
authors.lastname: Temirov
authors.affiliation: 1] Peter Grünberg Institut (PGI-3), Forschungszentrum Jülich, 52425 Jülich, Germany [2] Jülich Aachen Research Alliance (JARA)-Fundamentals of Future Information Technology, 52425 Jülich, Germany.
authors.forename: F Stefan
authors.initials: FS
authors.lastname: Tautz