He-atom scattering from MgO(100): calculating diffraction peak intensities with an ab initio potential
R. Martinez-Casado1, G. Mallia1, D. Usvyat2, L. Maschio3,4, S. Casassa3,4, M. Schuetz2 and N. M. Harrison1,5
1 Department of Chemistry, Thomas Young Centre, Imperial College, London SW7 2AZ, UK
2 Univ Regensburg, Inst Phys & Theoret Chem, D-93040 Regensburg, Germany
3 Univ Turin, Dipartimento Chim, IFM, I-10125 Turin, Italy
4 Univ Turin, Ctr Excellence NIS, I-10125 Turin, Italy
5 STFC, Daresbury Laboratory, Daresbury, Warrington WA4 4AD, UK
He-atom scattering from surfaces is a well established and valuable tool for characterizing the structure of periodic surfaces, determining gas-surface interaction potentials, and investigating the presence of defects and adsorbates. Unlike other techniques (e.g., LEED, STM or FIM), He-atom scattering causes no damage to the surface and it is very surface sensitive, as it probes only the outermost layer, and does not suffer from the surface charging effects, which plague, for instance, surface ion scattering, photoelectron spectroscopy and electron diffraction. He-atom scattering would be a very powerful technique for probing surface structure and dynamics if the measured spectra could be interpreted. The correct interpretation of the experimental scattering data requires an accurate description of the He-surface interaction potential. Empirical models of the potential, which introduce an uncontrolled approximation to the interpretation of the data, have been used but are limited to few systems, where interactions are reasonably well understood. A quantum-mechanical description of the interactions has not previously been possible, because the dominant methodologies for dealing with extended systems are based on Hartree-Fock (HF), density functional theory (DFT) and/or hybrid exchange DFT approaches, which do not describe correctly London dispersion forces, vital for the scattering process. In our most recent works [1,2,3,4], we show that a qualitatively correct description of the He-MgO interaction potential can be obtained by applying second order Rayleigh Schroedinger perturbation theory to calculate the correlation energy contribution to the London dispersion interaction based on,-single particle orbitals from either Hartree-Fock theory or hybrid-exchange density functional theory as the reference state.
[1] J. Chem. Phys. 134, 014706 (2011)
[2] Phys. Chem. Chem. Phys. 13, 14750 (2011)
[3] Chem. Comm. 47, 4385 (2011)
[4] Chem. Comm. 47, 11630 (2011)