What aspects of this project do you find most exciting? The application of bonding analysis methods from molecular chemistry to extended systems (surfaces, solids) provides an important insight into the driving forces of surface chemistry.F or arather large molecule as cyclooctyne, these methods allow to distinguish which effects are caused by the functional group, the molecular ring strain, and the sheer size of the molecule. Furthermore, the well-known failure of many DFT functionals in describing dis-persive interactions and the consequential need for dispersion correction terms turns out to be am ajor advantage. The ability to switch these interactions on and off enabled us to gain insight on the influence of dispersion effects on energy and structure of ad-sorption states. Who designed the cover? The cover was designed by Aaron Beller,astudent of fine arts at the University of Marburg. He specializes in 3D computer graphics and enjoys the challenge of visualizing scientific results in aw ay that is appealing, yet faithful to the content. What other topics are you working on at the moment? Besides investigating the bonding of chemisorbed states for organic molecules on semiconductor surfaces, we are also modelling the adsorption dynamics leading to these states. As can be expected, the large size of cyclooctyne molecules presents new challenges for methodology and concepts. What future opportunities do you see in the light of the results presented in this paper? The way in which cyclooctyne binds to the silicon surface makes it an ideal candidate for the construction of organic/semiconductor interfaces. By adding further functional groups to the ring, one might be able to introduce capabilities to semiconductor devices that are currently limited to molecular or biological systems (e.g., molecular recognition) and enhance their application range. We are currently working on this goal with other groups in Marburg in the framework of the collaborative research centre SFB 1083. Invited for the cover of this issue is the group of Ralf Tonner at the University of Marburg. Thei mage depicts the anchoring of cyclooctyne to aS i(001) surface. Read the full text of the article at

The gas-phase ozonolysis of cyclic-alkenes (1-methyl-cyclohexene, methylene-cyclohexane, α-pinene, β-pinene) is studied with respect to the pressure dependent formation of secondary organic aerosol (SOA). We find that SOA formation is substantially suppressed at lower pressures for all alkenes under study. The suppression coincides with the formation of ketene (α-pinene, 1-methyl-cyclohexene), ethene (1-methyl-cyclohexene) and the increased formation of CO (all alkenes) at lower reaction pressures. The formation of these products is independent of the presence of an OH scavenger and explained by an increased chemical activation of intermediate species in the hydroperoxide channel after the OH elimination. These findings underline the central role of the hydroperoxide pathway for SOA formation and give insight into the gas-phase ozonolysis mechanism after the stage of the Criegee intermediate chemistry.

What prompted you to investigate this problem? We set out to theoretically treat hindered motions for molecules adsorbing on as urface, an intriguing challenge for calculating the entropy loss upon adsorption.Wepicked aseemingly well-understood system,e thylene on Si(001), where the weakly bound precursor state was assumed to be mobile. When the barriers for diffusion on the surfacet urned out to be much higher than the reactionb arrier,w er ealized that some previous assumptions for this system needed to be reconsidered. This led us to investigatet he system in more detail. JosuaP echer Ralf To nner

Differences in adsorption and reaction energetics for ethylene on Si(001) are reported with respect to distorted dangling-bond configurations induced by hydrogen precoverage, as obtained by DFT calculations. This can help to understand the influence of surface defects and precoverage on the reactivity of organic molecules on semiconductor surfaces in general. The results show that the reactivity of surface dimers fully enclosed by hydrogen-covered atoms is essentially unchanged compared to the clean surface. This is confirmed by scanning tunneling microscopy measurements. On the contrary, adsorption sites with partially covered surface dimers show a drastic increase in reactivity. This is due to a lowering of the reaction barrier by more than 50 % relative to the clean surface, which is in line with previous experiments. Adsorption on dimers enclosed by molecule (ethylene)-covered surface atoms is reported to have a strongly decreased reactivity, as a result of destabilization of the intermediate state due to steric repulsion; this is quantified through periodic energy decomposition analysis. Furthermore, an approach for the calculation of Gibbs energies of adsorption based on statistical thermodynamics considerations is applied to the system. The results show that the loss in molecular entropy leads to a significant destabilization of adsorption states.

Chemical bonding concepts like covalency, ionicity, Pauli repulsion, shared-electron, or donor-acceptor bonding are important tools to sort our vast knowledge in chemistry and predict new reactivity. Electronic structure analysis provides the basis for a detailed understanding of the origins of these concepts. Energy decomposition analysis (EDA) is an established method for molecules and has recently been implemented for application in extended systems, that is, surfaces and solids, where it is termed periodic EDA (pEDA). The foundations and applications of this method which enables the derivation of bonding concepts are outlined in this review. Embedded in key examples from molecular and solid-state chemistry, the major part covers the adsorption and reactivity of molecules with surfaces with a focus on organic molecules interacting with semiconductor surfaces. Based on electronic structure analysis and supported by a quantitative methodology, we show that analogous bonding concepts can be applied in diverse chemical environments. This article is categorized under: Electronic Structure Theory > Ab Initio Electronic Structure Methods Structure and Mechanism > Computational Materials Science K E Y W O R D S chemical bonding, density functional theory, energy decomposition analysis, surface chemistry 1 | INTRODUCTIONThe chemical bond is the central concept in the discussion of structures and reactivity in chemistry. The nature of the forces that hold atoms together thrills chemists since the upcoming of atomistic theories. First realistic models were derived more than two centuries ago based on experimental observations. 1 The paradigm shift at the beginning of the 20th century then provided the basis for our present-day understanding of chemical bonding in terms of quantum mechanical principles. 2,3 But by no means did this development end the discussion about chemical bonding and the interpretation of results obtained by theory and computation. The intrinsic ambiguity in discussing often nonobservable properties that are connected to very useful concepts like covalency, ionicity, Pauli repulsion, bond order, and alike fosters the scientific discussion and leads to a further refinement of our understanding of the chemical bond. [4][5][6][7][8][9][10][11] The development of bonding concepts in molecular and solid-state chemistry evolved separately for the most part. For molecules, the view on (more or less) localized bonds as given by the Lewis picture more than a century ago 12 was regained both by valence bond (VB) theory and from the molecular orbital (MO) approach by the linear combination of atomic orbitals (LCAO) and localization procedures. [13][14][15][16] This resulted in the development of many powerful methods for electronic structure analysis for the qualitative and quantitative interpretation of chemical bonding that have been summarized in previous reviews. 2,17-21 Some examples will be discussed in the next section. In the field of surfaces and solids, the delocalized view