Kristian Berland, Per Hyldgaard, Chalmers University of Technology APS March meeting

1. Kristian Berland, Per Hyldgaard, Chalmers University of Technology APS March meeting March 18, 2013 A5: Analyzing the vdW-DF description of binding mechanisms: Comparison of C60 and benzene adsorption on graphene arxiv.org/abs/1303.0389

2. Compare benzene and C60 adsorption Same interface Different volume • Analyze vdW-DF • Compare vdW-DF variants K. Berland (berland@chalmers.se) P. Hyldgaard arxiv.org/abs/1303.0389

3. Benzene and C60 binding curves Difference between binding curve of benzene and C60: • vdW-DF1 stronger non-local correlation interaction than vdW-DF2 Semi-local part • C60 binds more than benzene • Results sensitive to functional version • vdW-DF1 binds more than vdW-DF2 non-local correlation part K. Berland (berland@chalmers.se) P. Hyldgaard arxiv.org/abs/1303.0389

4. Separation decomposition bz-graphene 3.6 Å) • Decompose non-local correlation Short separations: vdW-DF1 and vdW-DF2 similar C60 and benzene similar Long separations: Systems and vdW-DFs differ C60-graphene 3.6 Å) K. Berland (berland@chalmers.se) P. Hyldgaard arxiv.org/abs/1303.0389

5. Low-density regions dominate 2 % • Remove low-density regions first • Peel off 2 % of total density → 15% of van der Waals interaction lost • Peel off 8 % of total density → 65% of van der Waals interaction lost 8% Benzene-graphene sep. 3.0 Å K. Berland (berland@chalmers.se) P. Hyldgaard arxiv.org/abs/1303.0389 K. Berland (berland@chalmers.se) P. Hyldgaard arxiv.org/abs/1303.0389 K. Berland (berland@chalmers.se) P. Hyldgaard arxiv.org/abs/1303.0389

6. Site energy sensitivity Surface barriers very sensitive to functional variant K. Berland (berland@chalmers.se) P. Hyldgaard arxiv.org/abs/1303.0389

7. Sensitivity arise indirectly from separation • Surface barriers very sensitive to functional variant • Surface barriers insensitive to functional variant at given separation Functional Separation Surface Barriers K. Berland (berland@chalmers.se) P. Hyldgaard arxiv.org/abs/1303.0389

8. Summary • Benzene and C60 on graphene differ because of van der Waals forces • vdW-DF: several exchange-variants, two correlation versions • Non-local correlation of vdW-DF1 and vdW-DF2 similar for short density separations, differ at large. • Low-density regions essential for non-local correlation. • Surface site variation very sensitive to functional because functional sets separation Barriers Functional Separation Phys. Rev. B 84, 155451 (2011) Kristian Berland (berland@chalmers.se) arxiv.org/abs/1303.0389

9. Learning about xc-functional Functional • Learn about non-local correlation by comparing C60 and benzene • Use corrugation measurements to given learn about xc-functional Diffusion barriers Functional Separation Diffusion barriers K. Berland (berland@chalmers.se) P. Hyldgaard arxiv.org/abs/1303.0389

10. C60 dipole formation Small dipole on C60 on graphene Rich dipolar structure Small effect on binding (compare to adsorption on BN) Phys. Rev. B 84, 155451 (2011) K. Berland (berland@chalmers.se) P. Hyldgaard arxiv.org/abs/1303.0389

11. Adsorption results • BN and graphene similar • vdW-DF1 best adsorption energies • Optimal sites: bz on G: top(AB) bz on BN: top-N (AB) C60 on G: top-rot C60 on BN: top-N-rot • What do we learn? a) PRB. 69 155406 (2004) b) PRL. 90, 095501 (2003) K. Berland (berland@chalmers.se) P. Hyldgaard arxiv.org/abs/1303.0389

12. Low-density regions dominate • Introduce low-density cutoff • Relate to density fraction removed 1.6% 8% Benzene-graphene sep. 3.0 Å K. Berland (berland@chalmers.se) P. Hyldgaard arxiv.org/abs/1303.0389 K. Berland (berland@chalmers.se) P. Hyldgaard arxiv.org/abs/1303.0389 K. Berland (berland@chalmers.se) P. Hyldgaard arxiv.org/abs/1303.0389

13. xc-functionals contribution to binding curve • Separation mostly set by exchange-variant • Binding energy depends correlation version • Curves can be related to separation Kristian Berland (berland@chalmers.se) arxiv.org/abs/1303.0389