Towards an ab Initio, description of adsorbate vibrations

Chulkov, Sergey

November 2013

Thesis or dissertation

© 2013 Sergey Chulkov. All rights reserved. No part of this publication may be reproduced without the written permission of the copyright holder.

This thesis investigates accurate theoretical prediction of anharmonic vibrational frequencies of molecules adsorbed on metal surfaces. Such adsorbed systems are composed of two parts with dierent electronic properties, the adsorbate and the surface. However, most existing quantum mechanical methods are not identically accurate for both parts. Moreover, methods that can accurately describe extended system are very time consuming and signicantly complicates their usage for standard anharmonic calculations.

This thesis introduces a fragment method to overcome this difficulty. Within our method an energy correction is computed using high-level ab initio quantum mechanical method by considering an adsorbed molecule separately from the metal surface. The reliability of this approach is demonstrated for two test systems: an acetylene molecule adsorbed on a Cu(001) surface and a thiophene molecule adsorbed on a Au(111) surface. In both cases intra-adsorbate anharmonic frequencies obtained using the fragment method show better agreement with experimental data than the corresponding anharmonic frequencies computed using a standard approach. Moreover, a correlation between the accuracy of the fragment method and the accuracy of the ab initio method used for adsorbed molecule is observed. This correlation provides a way to systematically improve adsorbate frequencies by improving the quality of the potential energy surface used.

Finally, for each test systems we established a correlation between the strength of adsorption and the value of the frequencies shift upon adsorption. This allows us to conclude that terthiophene is only weakly adsorbed on a Au(111) surface based on the similarity between the adsorbate and the gas-phase vibrational spectra.

Department of Chemistry, The University of Hull
Sponsor (Organisation)
University of Hull; Deutsche Forschungsgemeinschaft
Qualification level
Qualification name
3 MB
QR Code