Sten Lunell

Adsorption of Bi-Isonicotinic Acid on Rutile TiO2 (110)

Bi-isonicotinic acid ~2,28-bipyridine–4,48-dicarboxylic acid! is the ligand of several organometallic dyes, used in photoelectrochemical applications. Therefore the atomic scale understanding of the bonding of this molecule to rutile TiO2(110) should give insight into the crucial dye–surface interaction. High resolution x-ray photoelectron spectroscopy ~XPS!, near edge x-ray absorption fine structure ~NEXAFS!, and periodic intermediate neglect of differential overlap ~INDO! calculations were carried out on submonolayer bi-isonicotinic acid rutile TiO2(110). Data from multilayers is also presented to support the submonolayer results. For a multilayer, XPS shows that the carboxyl groups remain in the ~pristine! protonated form, and NEXAFS show that the molecular plane is tilted by 57° with respect to the surface normal. For the submonolayer, the molecule bonds to the rutile TiO2(110) surface via both deprotonated carboxyl groups, with a tilt angle of 25°, and additionally an azimuthal orientation of 44° with respect to the @001# crystallographic direction. The adsorbant system was also investigated by quantum mechanical calculations using a periodic INDO model. The most stable theoretical adsorption geometry involves a twist around the molecular axis, such that the pyridine rings are tilted in opposite directions. Both oxygen atoms of each carboxyl group are bonded to five-fold coordinated Ti atoms ~2M-bidentate!, in excellent agreement with the experimental results.

Absorption and electrochemical properties of ruthenium(II) dyes, studied by semiempirical quantum chemical calculations

The electronic properties of Ru-polypyridine dyes were investigated by means of semiempirical calculations. Intermediate neglect of differential overlap (INDO)/S including configuration interaction (CI) was used to calculate electronic density of state (D

Recent Developments in Configuration Interaction and Density Functional Theory Calculations of Radical Hyperfine Structure.

Publisher Summary This chapter investigates two fundamentally different, yet complementary routes to computational studies of radical hyperfine structures. The role and importance of higher than double excitations in the configuration expansions has been elucidated by means of detailed case studies on a number of first row atoms, as well some selected molecular systems. The chapter later explored an alternative route to the calculation of radical hfs—namely the DFT-based approaches. Future applications of the DFT based hfcc calculations will involve extending the sets of systems into areas, such as surface chemistry, biophysics, and large transition metal complexes, where MRCI approaches again will serve as an extremely important tool for calibrating the calculations of the larger systems, to reveal possible pitfalls and explain deviations when these occur.

Computational Study of the Lowest Triplet State of Ruthenium Polypyridyl Complexes Used in Artificial Photosynthesis.

The potential energy surfaces of the first excited triplet state of some ruthenium polypyridyl complexes were investigated by means of density functional theory. Focus was placed on the interaction between the geometrical changes accompanying the photoactivity of these complexes when used as antenna complexes in artificial photosynthesis and dye-sensitized solar cells and the accompanying changes in electronic structure. The loss process (3)MLCT --> (3)MC can be understood by means of ligand-field splitting, traced down to the coordination of the central ruthenium atom.

N 1s x-ray absorption study of the bonding interaction of bi-isonicotinic acid adsorbed on rutile TiO2(110)

N 1s x-ray absorption spectra of bi-isonicotinic acid (2,2′-bipyridine–4,4′-dicarboxylic acid) on rutile TiO2(110) have been studied experimentally and quantum chemically. Differences between multilayer and monolayer spectra are explained by the adsorbate bonding to the substrate. A connection to the electronic coupling in dye-sensitized electrochemical devices is made.

Electronic interactions between aromatic adsorbates and metal oxide substrates calculated from first principles

The electronic structure of interfaces between aromatic adsorbates and metal oxide surfaces has been investigated using periodic hybrid ab initio Hartree–Fock-density functional theory calculations. Strong interfacial electronic coupling is observed for isonicotinic acid adsorbed on ZnO(1 0 0) and TiO2(1 1 0) surfaces. The results are in good agreement with experiments of ultrafast surface electron transfer processes for TiO2, and current experimental controversies regarding ZnO are clarified theoretically.

A theoretical and experimental study of the carbon 1s shake-up structure of benzene

Abstract The shake-up structure of the carbon 1s electron line in the spectrum of benzene has been studied by ESCA in high resolution and also theoretically, by means of the Pariser—Parr—Pople (PPP) method, including configuration interaction (CI). The calculated positions of the different shake-up lines relative to the main peak are found to be in surprisingly good agreement with experiment, the errors in excitation energies being a few per cent in all cases. On the basis of the calculations all observed lines in the spectrum can be assigned to excitations in the π system of the ionized molecule.

Photodissociation of Bromobenzene, Dibromobenzene, and 1,3,5-Tribromobenzene

Quantum chemical calculations have been performed on the ground state and several low-lying excited states of bromobenzene, ortho-, meta-, and para-dibromobenzene, and 1,3,5-tribromobenzene using high-level ab initio and hybrid density-functional methods. Experimental observations of ultrafast predissociation in these molecules are clarified from extensive theoretical information about all low-energy potential-energy curves together with symmetry arguments. The intriguing observation that o- and m-dibromobenzene have two ultrafast predissociation channels while bromobenzene, p-dibromobenzene, and 1,3,5-tribromobenzene only have one such channel is explained from the calculated potential-energy curves. These show that the lowering of point-group symmetry from C2v to Cs along the main photodissociation reaction coordinate, which only occurs in o- and m-dibromobenzene, opens up a new predissociation channel. Dynamical quantum simulations based on the calculated potential-energy curves are used to estimate the coupling strength at the intersystem crossing point in bromobenzene.

Periodic INDO Calculations of Organic Adsorbates on a TiO2 Surface

A new parametrization for use in periodic semiempirical quantum-chemical INDO calculations is proposed. Parameter sets for C and N atoms are tested on a number of C- and N-containing molecules, giving reasonably good agreement with experimental data and/or ab initio results. The new parametrization is intended for studies of organic adsorbates on oxide surfaces using a periodic large unit cell (LUC) model. As an example, two possible adsorption geometries for bi-isonicotinic acid on a TiO2 rutile(110) surface were investigated, and structural effects involved in the adsorption are discussed.

Quantum-chemical studies of metal oxides for photoelectrochemical applications

A review of recent research, as well as new results, are presented on transition metal oxide clusters, surfaces, and crystals. Quantum-chemical calculations of clusters of first row transition metal oxides have been made to evaluate the accuracy of ab initio and density functional calculations. Adsorbates on metal oxide surfaces have been studied with both ab initio and semi-empirical methods, and results are presented for the bonding and electronic interactions of large organic adsorbates, e.g. aromatic molecules, on Ti02 and ZnO. Defects and intercalation, notably of H, Li, and Na in Ti02 have been investigated theoretically. Comparisons with experiments are made throughout to validate the calculations. Finally, the role of quantum-chemical calculations in the study of metal oxide based photoelectrochemical devices, such as dyesensitized solar cells and electrochromic displays. is discussed.