Recent STM experiments have reported a surprising chiral behavior of intrinsically achiral organic molecules when adsorbed on a metal surface: at around 400K, succinic acid molecules adsorbed on Cu(110) formed two thermally stable and asymmetric superstructures, in which succinate trimers extend in rows along the [-112] and [1-12] directions [1]. In this study, we aim at an atomistic understanding of the nature of this intriguing ordering process, which appears as a suitable model system for the development of future enantio-selective heterogeneous catalysts. A systematic theoretical investigation reveals that the intermolecular interactions between succinates cannot be accurately described by density-functional theory calculations alone, since molecular adsorptions in this case are leading to local charge reorganization, rendering the total interaction energy effectively zero. However, analyzing the charge redistribution and determining the ensuing quadrupole moments, we find that quadrupole interactions may contribute to interaction energies of up to hundreds of meV. Determining the molecular adsorbates by density functional theory, and complementing the structural information with quadrupole interaction energies, we employed a parameterized lattice gas Hamiltonian approach, addressing the mesoscopic ordering at finite temperatures by means of Monte Carlo simulations [2]. Here, we find that the quadrupole interactions are the key to understanding the observed molecular patterns.
[1] V. Humblot, M.O. Lorenzo, G.J. Baddeley, S. Haq and R. Raval J. Am. Chem. Soc. 126, 6460 (2004)
[2] K. Reuter, C. Stampfl, and M. Scheffler, Ab initio atomistic thermodynamics and statistical mechanics of surface properties and functions, in : Handbook of Materials Modeling, Vol. 1, (Ed.) S. Yip. Kluwer, Dordrecht (2005)
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