Selective Adsorption of a Supramolecular Structure on Flat and Stepped Gold Surfaces

Halogenated aromatic molecules assemble on surfaces forming both hydrogen and halogen bonds. Even though these systems have been intensively studied on flat metal surfaces, high-index vicinal surfaces remain challenging, as they may induce complex adsorbate structures. The adsorption of 2,6-dibromoanthraquinone (2,6-DBAQ) on flat and stepped gold surfaces is studied by means of van der Waals corrected density functional theory. Equilibrium geometries and corresponding adsorption energies are systematically investigated for various different adsorption configurations.~It is shown that bridge sites and step edges are the preferred adsorption sites for single molecules on flat and stepped surfaces, respectively. The role of van der Waals interactions, halogen bonds and hydrogen bonds are explored for a monolayer coverage of 2,6-DBAQ molecules, revealing that molecular flexibility and intermolecular interactions stabilize two-dimensional networks on both flat and stepped surfaces. Our results provide a rationale for experimental observation of molecular carpeting on high-index vicinal surfaces of transition metals.Comment: Preprint. 24 pages, 5 figure

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Components of the response function of a high-purity germanium (HPGe) detector due to full or partial energy deposition by gamma- and X-rays were studied. Experimental response functions for 241Am, Ba and Tb were compared with those obtained from the Monte Carlo simulations. The role of physical mechanisms for each component was investigated by considering escape/absorption of photons, photoelectrons, Auger electrons, recoil electrons and X-rays of the detector material. A detailed comparison of the experimental Compton, photoelectron, detector X-ray escape components and full-energy peaks with those obtained from Monte Carlo program are presented.M.S. - Master of Scienc

Nanosistemlerde lityum-karbon etkileşmeleri: moleküler dinamik modellemeler ve yoğunluk fonksiyonu teoremi hesapları

Single walled carbon nanotubes have been attracting interest for their electronic, magnetic, chemical and mechanical properties. Moreover, since they are ideal nano-containers, the adsorption and absorption properties provide them to be used as Li/Li+ ion batteries. The capacity, rate capability and cycle life of the batteries are the important points which must be improved to have better results. In this thesis Li/Li+ ion doped carbon nano structures are investigated theoretically in order to contribute to the lithium battery technology. The present studied carbon nano structures are the fullerenes, single-walled carbon nanotubes, pristine and defected (Stone-Wales and mono-vacancy defected) carbon nanocapsules. The Li/Li+ interactions with these nano structures have been investigated using semi-empirical molecular orbital method at PM3 level, density functional theory method with B3LYP exchange-correlation functional using 3-21G or 6-31G basis sets. Furthermore, the systems have been investigated by molecular dynamics simulations in which Tersoff potential and an empirical many-body potential have been used to define the various interactions. In this thesis the optimized geometries, thermodynamical quantities, interfrontier molecular orbital eigenvalues and dipole moments of the studied systems have been reported.Ph.D. - Doctoral Progra

Effect of van der Waals interactions on the chemisorption and physisorption of phenol and phenoxy on metal surfaces.

The adsorption of phenol and phenoxy on the (111) surface of Au and Pt has been investigated by density functional theory calculations with the conventional PBE functional and three different non-local van der Waals (vdW) exchange and correlation functionals. It is found that both phenol and phenoxy on Au(111) are physisorbed. In contrast, phenol on Pt(111) presents an adsorption energy profile with a stable chemisorption state and a weakly metastable physisorbed precursor. While the use of vdW functionals is essential to determine the correct binding energy of both chemisorption and physisorption states, the relative stability and existence of an energy barrier between them depend on the semi-local approximations in the functionals. The first dissociation mechanism of phenol, yielding phenoxy and atomic hydrogen, has been also investigated, and the reaction and activation energies of the resulting phenoxy on the flat surfaces of Au and Pt were discussed

Effect of van der Waals interactions on the chemisorption and physisorption of phenol and phenoxy on metal surfaces.

The adsorption of phenol and phenoxy on the (111) surface of Au and Pt has been investigated by density functional theory calculations with the conventional PBE functional and three different non-local van der Waals (vdW) exchange and correlation functionals. It is found that both phenol and phenoxy on Au(111) are physisorbed. In contrast, phenol on Pt(111) presents an adsorption energy profile with a stable chemisorption state and a weakly metastable physisorbed precursor. While the use of vdW functionals is essential to determine the correct binding energy of both chemisorption and physisorption states, the relative stability and existence of an energy barrier between them depend on the semi-local approximations in the functionals. The first dissociation mechanism of phenol, yielding phenoxy and atomic hydrogen, has been also investigated, and the reaction and activation energies of the resulting phenoxy on the flat surfaces of Au and Pt were discussed

Adsorption of dichlorobenzene on Au and Pt stepped surfaces using van der Waals density functional theory

The adsorption of dichlorobenzene on flat (111) and stepped (332) Au and Pt surfaces was studied using density functional theory with both a conventional generalized gradient approximation (GGA) and a fully nonlocal van der Waals density functional (vdW-DF). The equilibrium geometries and adsorption energies were computed for several different adsorption configurations. The two functionals yielded qualitatively different results, with the GGA functional predicting only weak binding compared to vdW-DF, demonstrating the importance of including nonlocal dispersion. By analyzing the electronic density and projected density of states, it was found that the interaction of dichlorobenzene with the two surfaces caused a charge redistribution, especially for the stepped surfaces. Moreover, adsorption on the step edge on Au(332) was dominated by nonlocal dispersion, whereas adsorption on the Pt(332) step was dominated by chemical bonding