Computational physics and chemistry at CCMS

Abstract: I will show a selection of projects currently under way at the CCMS, namely 1) calculation of electronic gaps in 2D materials, and 2) modeling of creation of magnetic nanostructures, adsorbed Co atoms on the p(2x1) Cu(110):O surface, by low-temperature non-contact atomic force microscopy manipulation in UHV.

In 1), based on our study of few-layer phosphorene [1], I will show, using ultra accurate Quantum Monte Carlo method, what we believe are the most accurate gap estimates and highlight the challenges encountered if gap estimates with accuracy higher than ≈0.1 eV are required.

In 2), using DFT calculations with Hubbard U correction, we have modelled two very different lateral Co manipulations, namely the fairly straightforward lateral manipulation by one lattice site, figure a-b) and a delocalization manipulation where the Co adatom followed a smeared-out manipulation trajectory with the Co atom delocalized over roughly six substrate Cu atoms, figure c). This latter delocalized state remained (meta)stable over macroscopic time. The calculated PES, figure d), indicates very weak corrugation in some parts and very substantial corrugation in other parts. The calculations show that the tip-assisted delocalization manipulation is a consequence of [Ar]d8 → [Ar]d7 modification of the spin state of the manipulated Co atom rendering it less reactive and hence more easy to manipulate, a fact which may have spintronics consequences. However, in order to rationalize the experimentally observed elliptical manipulation trajectories, an additional modulating potential is needed. We argue that this long-ranged modulation potential is created via Friedel oscillations [3] of the metal charge densities generated by the other Co atoms present on the surface. These additional Co atoms are repositionable by ordinary lateral manipulations giving access to different delocalization scenarios. Fig. Experimental images of the “delocalization” c), and lateral manipulation, a-b), of a Co atom and the corresponding calculated PES, d), exhibiting both extremely weakly corrugated (<0.2eV; red and blue lines) and heavily corrugated (≈2eV; green and brown lines) portions.

[1] A. Castellanos-Gomez, J. Phys. Chem. Lett. 6, 4280 (2015).
[2] Y. Kinoshita et al., submitted to Nano Lett. (2016).
[3] P. Hyldgaard and M. Persson. J. Phys.: Condens. Matter 12, L13 (2000).