Program

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Tuesday June 23

Tu2: Surface diffusion and migration

Chair: J. Manson, Clemson, USA

Contributed talk

Diffraction of helium on MgO(100) calculated from first-principles

R. Martinez-Casado¹, D. Usvyat², G. Mallia³, L. Maschio⁴, S. Casassa⁴, J. Ellis⁵, M. Schütz², and N.M. Harrison^3,6

¹Departamento de Fisica Teorica de la Materia Condensada, Universidad Autonoma de Madrid, E-28049 Madrid, Spain

²Institut für Physikalische und Theoretische Chemie, Universität Regensburg, Universitätsstrasse 31, 93040 Regensburg, Germany

³Thomas Young Centre, Department of Chemistry, Imperial College London, South Kensington London SW7 2AZ, UK

⁴ Dipartimento di Chimica, Università degli Studi di Torino, I-10125 Turin, Italy

⁵Cavendish Laboratory, University of Cambridge, JJ Thomson Avenue, Cambridge, CB3 0HE, UK

⁶Daresbury Laboratory, Daresbury, Warrington, WA4 4AD, UK

Interactions between molecules and crystalline surfaces are of great fundamental and technological interest and extensively studied both experimentally and theoretically. The scattering of He atom beams on crystal surfaces has the potential to be an important technique for determining the atomistic structure and dynamics of surfaces. The He beam scatters from only the outermost surface layers unlike X-ray diffraction and it neither damages or charges the surface unlike electron diffraction and microscopy. During the last two decades its usefulness has been demonstrated in the determination of numerous surface structures. The quantitative interpretation of He-diffraction is, however, limited as the He–surface interaction potential is not known accurately. In our most recent works[1,2], we simulate the diffraction peak intensities of He beams scattered on the MgO(100) surface from first principles. Achieving the required accuracy in first-principles calculations is very challenging indeed. We describe a first principles protocol able to achieve very high accuracy for reasonable computational cost. This method is based on periodic local second-order Moller–Plesset perturbation theory where systematic corrections for basis set truncation and for high-order electronic correlation are introduced using coupled cluster calculations on finite model systems mimicking the target system. For the He–MgO system the requirements with respect to the level of theory are very high; it turns out that contributions from connected quadruple excitations are non-negligible. By using this protocol, it is possible to reach the accuracy in the He–MgO potential that is required to predict the observed He diffraction peak intensities.

[1] R. Martinez-Casado et al, Phys. Chem. Chem. Phys. 16, 21106 (2014)

[2] R. Martinez-Casado et al, Phys. Rev. B 89, 1098 (2014)