A series of 20 halogen bonded complexes of the types R-Br center dot center dot center dot Br- (R is a substituted methyl group) and R '-CC-Br center dot center dot center dot Br- are investigated at the M06-2X/6-311+G(d,p) level of theory. Computations using a point-charge (PC) model, in which Br- is represented by a point charge in the electronic Hamiltonian, show that the halogen bond energy within this set of complexes is completely described by the interaction energy (E-PC) of the point charge. This is demonstrated by an excellent linear correlation between the quantum chemical interaction energy and E-PC with a slope of 0.88, a zero intercept, and a correlation coefficient of R-2=0.9995. Rigorous separation of E-PC into electrostatics and polarization shows the high importance of polarization for the strength of the halogen bond. Within the data set, the electrostatic interaction energy varies between 4 and-18kcal mol(-1), whereas the polarization energy varies between -4 and-10kcal mol(-1). The electrostatic interaction energy is correlated to the sum of the electron-withdrawing capacities of the substituents. The polarization energy generally decreases with increasing polarizability of the substituents, and polarization is mediated by the covalent bonds. The lower (more favorable) E-PC of CBr4---Br- compared to CF3Br center dot center dot center dot Br- is found to be determined by polarization as the electrostatic contribution is more favorable for CF3Br center dot center dot center dot Br-. The results of this study demonstrate that the halogen bond can be described accurately by electrostatics and polarization without any need to consider charge transfer.

The current status of the molecular surface property approach (MSPA) and its application for analysis and prediction of intermolecular interactions, including chemical reactivity, are reviewed. The MSPA allows for identification and characterization of all potential interaction sites of a molecule or nanoparticle by the computation of one or more molecular properties on an electronic isodensity surface. A wide range of interactions can be analyzed by three properties, which are well-defined within Kohn-Sham density functional theory. These are the electrostatic potential, the average local ionization energy, and the local electron attachment energy. The latter two do not only reflect the electrostatic contribution to a chemical interaction, but also the contributions from polarization and charge transfer. It is demonstrated that the MSPA has a high predictive capacity for non-covalent interactions, for example, hydrogen and halogen bonding, as well as organic substitution and addition reactions. The latter results open u p applications within drug design and medicinal chemistry. The application of MSPA has recently been extended to nanoparticles and extended surfaces of metals and metal oxides. In particular, nanostructural effects on the catalytic properties of noble metals are rationalized. The potential for using MSPA in rational design of heterogeneous catalysts is discussed.

The Cu2O(100) surface is most favorably terminated by a (3,0;1,1) reconstruction under ultrahigh-vacuum conditions. As most oxide surfaces, it exhibit defects, and it is these sites that are focus of attention in this study. The surface defects are identified, their properties are investigated, and procedures to accurately control their coverage are demonstrated by a combination of scanning tunneling microscopy (STM) and simulations within the framework of density functional theory (DFT). The most prevalent surface defect was identified as an oxygen vacancy. By comparison of experimental results, formation energies, and simulated STM images, the location of the oxygen vacancies was identified as an oxygen vacancy in position B, located in the valley between the two rows of oxygen atoms terminating the unperturbed surface. The coverage of defects is influenced by the surface preparation parameters and the history of the sample. Furthermore, using low-energy electron beam bombardment, we show that the oxygen vacancy coverage can be accurately controlled and reach a complete surface coverage (1 per unit cell or 1.8 defects per nm(2)) without modification to the periodicity of the surface, highlighting the importance of using local probes when investigating oxide surfaces.

The potential energy surfaces in gas phase and in aqueous solution for the nitration of benzene, chlorobenzene, and phenol have been elucidated with density functional theory at theM06-2X/6-311G(d,p) level combined with the polarizable continuum solvent model (PCM). Three reaction intermediates have been identified along both surfaces: the unoriented pi-complex (I), the oriented reaction complex (II), and the sigma-complex (III). In order to obtain quantitatively reliable results for positional selectivity and for modeling the expulsion of the proton, it is crucial to take solvent effects into consideration. The results are in agreement with Olah's conclusion from over 40 years ago that the transition state leading to (II) is the rate-determining step in activated cases, while it is the one leading to (III) for deactivated cases. The simplified reactivity approach of using the free energy for the formation of (III) as a model of the rate-determining transition state has previously been shown to be very successful for halogenations, but problematic for nitrations. These observations are rationalized with the geometric and energetic resemblance, and lack of resemblance respectively, between (III) and the corresponding rate determining transition state. At this level of theory, neither the sigma-complex (III) nor the reaction complex (II) can be used to accurately model the rate-determining transition state for nitrations.

The halogenation of monosubstituted benzenes in aqueous solvent was studied using density functional theory at the PCM-M06-2X/6-311G(d,p) level. The reaction with Cl-2 begins with the formation of C atom coordinated pi-complex and is followed by the formation of the sigma-complex, which is rate-determining. The final part proceeds via the abstraction of the proton by a water molecule or a weak base. We evaluated the use of the sigma-complex as a model for the rate-determining transition state (TS) and found that this model is more accurate the later the TS comes along the reaction coordinate. This explains the higher accuracy of the model for halogenations (late TS) compared to nitrations (early TS); that is, the more deactivated the substrate the later the TS. The halogenation with Br-2 proceeds with a similar mechanism as the corresponding chlorination, but the bromination has a very late rate-determining TS that is similar to the sigma-complex in energy. The iodination with ICl follows a different mechanism than chlorination and bromination. After the formation of the pi-complex, the reaction proceeds in a concerted manner without a sigma-complex. This reaction has a large primary hydrogen kinetic isotope effect in agreement with experimental observations.

The initial steps of Cu₂O sulphidation to Cu₂S have been studied using plane-wave density functional theory at the PBE-D3+U level of sophistication. Surface adsorption and dissociation of H₂S and H₂O, as well as the replacement reaction of lattice oxygen with sulphur, have been investigated for the most stable (111) and (100) surface facets under oxygen-lean conditions. We find that the (100) surface is more susceptible to sulphidation than the (111) surface, promoting both H₂S adsorption, dissociation and the continued oxygen–sulphur replacement. The results presented in this proceeding bridge previous results from high-vacuum experiments on ideal surface to more realistic corrosion conditions and set the grounds for future mechanistic studies. Potential implications on the long-term final disposal of spent nuclear fuel are discussed.

Adsorption and desorption of methanol on the (111) and (100) surfaces of  Cu2O have been studied using high-resolution photoelectron spectroscopy in the temperature range 120–620 K, in combination with density functional theorycalculations and sum frequency generation spectroscopy. The bare (100) surfaceexhibits a (3,0; 1,1) reconstruction but restructures during the adsorption process into a Cu-dimer geometry stabilized by methoxy and hydrogen binding in Cu-bridge sites. During the restructuring process, oxygen atoms from the bulk that can host hydrogen appear on the surface. Heating transforms methoxy to formaldehyde, but further dehydrogenation is limited by the stability of the surface and the limited access to surface oxygen. The (√3 × √3)R30°-reconstructed (111) surface is based on ordered surface oxygen and copper ions and vacancies, which offers a palette of adsorption and reaction sites. Already at 140 K, a mixed layer of methoxy, formaldehyde, and CHxOy is formed. Heating to room temperature leaves OCH and CHx. Thus both CH-bond breaking and CO-scission are active on this  surface at low temperature. The higher ability to dehydrogenate methanol on (111) compared to (100) is explained by the multitude of adsorption sites and, in particular, the availability of surfaceoxygen.

Crystalline surfaces of gold are chemically inert, whereas nanoparticles of gold are excellent catalysts for many reactions. The catalytic properties of nanostructured gold have been connected to increased binding affinities of reactant molecules to low-coordinated Au atoms. Here we show that the high reactivity at these sites is a consequence of the formation of σ-holes, i.e. maxima in the surface electrostatic potential (Vs,max) due to the overlap of mainly the valence s-orbitals when forming the bonding σ-orbitals. The σ-holes are binding sites for Lewis bases, and binding energies correlate with magnitudes of the Vs,max. For symmetrical Au clusters, of varying size, the most positive Vs,max are found at corners, edges, and surfaces (facets) and decreasing in that order. This is in agreement with the experimentally and theoretically observed dependence of catalytic activity on local structure. The density of σ-holes can explain the increasing catalytic activity with decreasing particle size also for other transition metal catalysts, such as platinum.

Transition metal oxide nanoparticles are common materials in a multitude of applications including heterogeneous catalysis, solar energy harvesting, and energy storage. Understanding the particles' interplay with their surroundings is key to their efficient usage and design. Herein two DFT-based descriptors are used to study local reactivity on (TiO2)(n) (n = 7-10) nanoparticles. The local electron attraction energy [E(r)] and the electrostatic potential [V(r)], evaluated on isodensity surfaces, are able to identify and rank Lewis acidic sites on the particles with high accuracy when compared to the interaction energies of the Lewis bases H2O, H2S, NH3, and CO. These interactions are characterized as mainly electrostatically controlled. Given the local character, low computational cost, and excellent performance of the E-s(r) and V-s(r) descriptors, they are anticipated to find widespread use in nanoparticle research and development.