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Bound by long-range interactions: Molecular crystals and benzene on Cu(111)

Kristian Berland (Institutionen för mikroteknologi och nanovetenskap, Bionanosystem)
: Chalmers University of Technology, 2009. - 94 s.
[Licentiatavhandling]

This thesis investigates molecular systems bound by long-range interactions. We study molecular crystals held together by van der Waals forces and the physisorption of benzene (Bz) on Cu(111). We also study the self-organization of benzene on the Cu(111) surface which is influenced both by the (semi) long-range van der Waals forces, and the very-long-ranged indirect electronic interactions mediated by a metallic surface state on the Cu(111) surface. The van der Waals bound systems are investigated from first-principle principles using a van der Waals density functional (vdW-DF), [Phys. Rev. Lett. 92, 246401 (2004)]. We examine the character of these interactions, by studying the asymptotic account of the van der Waals forces, and compare full vdW-DF with an asymptotic atom-based pair potentials extracted from vdW-DF. The results show that the charac- ter of the binding differs in the two cases, with vdW-DF being significantly enhanced at relevant binding separations. This suggests that the use of asymptotic atom-based pair potentials as an approximation for non-local correlation is not consistent. For molecular crystals, we study the structure and cohesive energy of hexamine and the platonic hydrocarbons cubane and dodecahedrane. The calculated lattice parame- ters and cohesion energy agree well with experiments. For adsorption of benzene on Cu(111), we obtain a binding energy in good agreement with experiment. We also study diffusion barriers and find that the molecules can move almost freely along a honeycomb web of “corridors” passing between fcc and hcp hollow sites via bridge sites. To account for the surface-state mediated interactions, we use a formal Harris-functional approach to evaluate nonperturbationally the asymptotic form of this in- direct interaction. This description is based on input from DFT calculations of the metallic surface state on Cu(111), in addition to a parameterization of the benzene- induced scattering properties. We combine vdW-DF calculations of benzene dimers and diffusion barriers with the estimates of the surface-state mediated interactions and find that the more compact (hexagonal) Bz-overlayer phase, with lattice constant ̊ a = 6.74 A, is due to direct Bz-Bz vdW attraction, and the stability of the sparser hexagonal Bz phase, a = 10.24 A, is due to surface-state mediated interactions. Thus, we can account well for benzene self-organization on Cu(111). These results illustrate the current state of development of quantum-physical based approaches to systems bound by long-range interactions.

Nyckelord: electronic structure, DFT, van der Waals density functional (vdW-DF), van der Waals forces, London-dispersion forces, sparse matter, soft matter, molecular crystals, platonic hydrocarbons, hexamine, physiosorption, diffusion barriers, surface-mediated interactions, Friedel oscillations, self-assembly, molecular overlayers



Denna post skapades 2009-11-27. Senast ändrad 2017-10-03.
CPL Pubid: 102344

 

Institutioner (Chalmers)

Institutionen för mikroteknologi och nanovetenskap, Bionanosystem (2007-2015)

Ämnesområden

Ytor och mellanytor
Elektronstruktur
Mesoskopisk fysik
Beräkningsfysik
Kemisk fysik

Chalmers infrastruktur

Relaterade publikationer

Inkluderade delarbeten:


Rings sliding on a honeycomb network: Adsorption contours, interactions, and assembly of benzene on Cu(111)


Examination

Datum: 2009-12-17
Tid: 13:15
Lokal: Fasrummet, MC2
Opponent: Sture Nordholm