Berlin 2012 – wissenschaftliches Programm
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O: Fachverband Oberflächenphysik
O 44: Focussed session: Functional molecules at surfaces II
O 44.7: Vortrag
Mittwoch, 28. März 2012, 12:30–12:45, A 053
First-principles study of redox-molecular switch above a polar thinfilm: a van der Waals + U description — •John Sharp, Felix Hanke, and Mats Persson — University of Liverpool, Liverpool, UK
A redox-type molecular switch functions by coupling the charging and discharging of a molecule to an obvious change in conformation. Such a switch was recently demonstrated experimentally, by investigating the molecule bis-dibenzoylmethanato-copper(II) (Cu(dbm)2) adsorbed on an ultra-thin insulating layer above a Cu substrate[1]. Here we aim to understand the molecular adsorption and switching properties using a first principles density functional approach to investigate the electronic structure of the complex. This investigation is challenging due to the van der Waals dominated adsorption and the presence of highly-correlated d-electrons in Cu(dbm)2. Here we use a van der Waals density functional [2] and a ‘GGA+U’ term to properly address these issues. Crystal field splitting of the d-orbitals underlies the conformational change that occurs upon charging, and the magnitude of the splitting is affected by the value of ‘U’ used. The experimentally observed changes in conformation upon charging the adsorbate are only reproduced with a self-consistently determined value of U. Moreover without inclusion of the U term a spontaneous charging of the adsorbate is observed even for the experimentally neutral configuration. Finally, we present scanning tunnelling microscopy simulations and compare the results with the experimentally available data.
[1] PRL 106 216103 (2011); [2] PRB 83 195131 (2011)