Dr. Wei Liu, Theory Department, Fritz-Haber-Institut der MPG, Berlin, Germany

Concerted Effects of Covalent Bonding and van der Waals Interactions in Hybrid Inorganic Organic Systems

The understanding of electronic properties of complex organic/metal interfaces requires a reliable method for the prediction of their structure and stability. The bonding at complex interfaces arises from delicate balance between covalent bonds, van der Waals (vdW) forces, charge transfer, and Pauli repulsion. Recently, we developed a method based on density-functional theory (DFT) with vdW interactions (DFT+vdW^surf [1]) to accurately model adsorbates on surfaces, by a synergetic linkage of the PBE+vdW method [2] for intermolecular interactions with the Lifshitz-Zaremba-Kohn theory [3] for the dielectric screening within the substrate surface. This method is demonstrated to reliably model a multitude of small and large molecules on metal surfaces [4], leading to an accuracy of 0.1 Å in adsorption heights and 0.1 eV in binding energies with respect to state-of-the-art experiments. In addition, our DFT+vdW^surf calculations lead to a few peculiar findings: (1) The vdW energy can contribute more to the binding of covalently bonded systems than it does in physisorbed interfaces [5,6]; (2) the binding energies of similar molecules can be identical, despite significantly different adsorption heights [7]; (3) the physically bound (precursor) state for aromatics on Pt(111) can be prominently stabilized and long-lived, making it potentially useful in molecular switches [8].

References:

1. V.G. Ruiz, W. Liu, E. Zojer, M. Scheffler, and A. Tkatchenko, Phys. Rev. Lett.108, 146103 (2012).
2. A. Tkatchenko and M. Scheffler, Phys. Rev. Lett.102, 073005 (2009).
3. E. Zaremba and W. Kohn, Phys. Rev. B13, 2270 (1976).
4. W. Liu, A. Tkatchenko, and M. Scheffler, Acc. Chem. Res. (2014), DOI: 10.1021/ar500118y.
5. W. Liu, et al., Phys. Rev. B 86, 245405 (2012).
6. W. Liu, et al., New J. Phys.15, 053046 (2013).
7. B. Schuler, W. Liu, et al., Phys. Rev. Lett.111, 106103 (2013).
8. W. Liu, et al., Nature Commun. 4, 2569 (2013).

Biography:

Wei Liu obtained his Ph.D. in materials science in 2009 at the Jilin University, China. In 2007, he was awarded a scholarship from Ministry of Education of China to pursue the study in University of California, Davis for a period of 24 months. During 2011−2013, he was an Alexander von Humboldt Fellow in the Theory Department of the Fritz Haber Institute (FHI) in Berlin. He is currently a research scientist at FHI. He has published 36 SCI papers, including Acc. Chem. Res., Nature Commun., and Phys. Rev. Lett., with more than 850 citations. 

By using density-functional theory and ab initio molecular dynamics, his research mainly focuses on:

1. Accurate prediction of adsorption geometries and binding energies for organic/inorganic interfaces;
2. Role of van der Waals interactions in adsorption systems;
3. Catalytic reactions of molecules on metal surfaces and clusters;
4. Simulation of atomic force microscopy and scanning tunneling microscopy images.