In this work, a new partitioning method is presented which allows one to calculate properties of radicals, in particular, atomic spin populations. The method can be seen as an extension of the Hirshfeld-I method [ Bultinck , P. et al. J. Chem. Phys. 2007 , 126 , 144111 ], in which the atomic weight functions, defining the atoms-in-molecules, are constructed by means of an iterative scheme in which the charges of the atoms-in-molecules are altered but the spin remains fixed. The Hirshfeld-I method is therefore not suitable for the calculation of atomic spin populations of open-shell systems. The new fractional occupation Hirshfeld-I (FOHI) uses an iterative scheme in which both the atomic charge and spin are optimized, resulting in a self-consistent method for the calculation of atomic spin populations. The results obtained with the FOHI method are compared with experimental results obtained using polarized neutron diffraction, thus serving as a validation of the FOHI method as well as the Hirshfeld definition of atoms-in-molecules in general.

A DFT study on the adsorption of a series of phosphonic acids (PAs) on the TiO2 anatase (101) and (001) surfaces was performed. The adsorption energies and geometries of the most stable binding modes were compared to literature data and the effect of the inclusion of dispersion forces in the energy calculations was gauged. As the (101) surface is the most exposed surface of TiO2 anatase, the calculated chemical shifts and vibrational frequencies of PAs adsorbed on this surface were compared to experimental 31 P and 17 O NMR and IR data in order to assign the two possible binding modes (mono-and bidentate) to peaks and bands in these spectra; due to the corrugated nature of anatase (101) tridentate binding is not possible on this surface. Analysis of the calculated and experimental 31 P chemical shifts indicates that both monodentate and bidentate binding modes are present. For the reactive (001) surface, the results of the calculations indicate that both bi-and tridentate binding modes are possible. Due to the particular sensitivity of 17 O chemical shifts to hydrogen bonding and solvent effects, the model used is insufficient to assign these spectra at present. Comparison of calculated and experimental IR spectra leads to the conclusion that IR spectroscopy is not suitable for the characterization of the different binding modes of the adsorption complexes.

The electron ionization mass spectra of four organic compounds are predicted based on the results of quantum chemical calculations at the DFT/B3LYP/6-311 + G* level of theory. This prediction is performed 'ab initio', i.e. without any prior knowledge of the thermodynamics or kinetics of the reactions under consideration. Using a set of rules determining which routes will be followed, the fragmentation of the molecules' bonds and the complete resulting fragmentation pathways are studied. The most likely fragmentation pathways are identified based on calculated reaction energies ΔE when bond cleavage is considered and on activation energies ΔE when rearrangements are taken into account; the final intensities of the peaks in the spectrum are estimated from these values. The main features observed in the experimental mass spectra are correctly predicted, as well as a number of minor peaks. In addition, the results of the calculations allow us to propose fragmentation pathways new to empirical mass spectrometry, which have been experimentally verified using tandem mass spectrometry measurements. Copyright © 2016 John Wiley & Sons, Ltd.

The evaluation of dispersion interaction energies, with the goal of correcting the performance of density functional theory (DFT) methods, is currently a topic of intensive research. Most of the dispersion-corrected DFT methods (DFT-D) rely on an additive correction expression based on the use of isotropic dispersion coefficients. This, however, undermines an important aspect of the interaction, i.e., its anisotropic nature. We demonstrate that, for systems of sufficient size, such as benzene dimers and DNA base pairs, the inclusion of anisotropy, through the use of the Hirshfeld method, results in an increase of dispersion energy values by up to 30%.

No abstract

In this work, we present a novel model, referred to as BH-DFT-D, for the evaluation of London dispersion, with the purpose to correct the performance of local DFT exchange-correlation functionals for the description of van der Waals interactions. The new BH-DFT-D model combines the equations originally derived by Buckingham [Buckingham, A. D. Adv. Chem. Phys1967, 12, 107] with the definition of distributed multipole polarizability tensors within the Hirshfeld method [Hirshfeld, F.L. Theor. Chim. Acta1977, 44, 129], resulting in nonlocal, fully anisotropic expressions. Since no damping function has been introduced yet into the model, it is suitable in its present form for the evaluation of dispersion interactions in van der Waals dimers with no or negligible overlap. The new method is tested for an extended collection of van der Waals dimers against high-level data, where it is found to reproduce interaction energies at the BH-B3LYP-D/aug-cc-pVTZ level with a mean average error (MAE) of 0.20 kcal/mol. Next, development steps of the model will consist of adding a damping function, analytical gradients, and generalization to a supramolecular system.

In this work, the partitioning of higher multipole polarizabilities, such as dipole-quadrupole, quadrupole-dipole, and quadrupole-quadrupole polarizabilities, into atomic contributions is studied. Partitioning of higher multipole polarizabilities is necessary in the study of accurate interaction energies where dispersion interactions are of importance. The fractional occupation Hirhsfeld-I (FOHI) method is used to calculate the atomic polarizabilities and is briefly explained together with the methodology for partitioning of the polarizabilities. The atomic multipole polarizabilities are calculated for different sets of molecules, linear alkanes, water clusters, and small organic molecules with different functional groups. It is found that the atomic and group contributions of the dipole and quadrupole polarizabilities are transferable as a function of the functional groups.

Based on research amongst Brazilian and Moroccan temporary residents of the cities of Brussels and Antwerp (Belgium), this article engages with the changes in and current methodological approaches to migration studies. By demonstrating how the trajectories of many contemporary migrants are marked by ongoing mobility, it further complicates previous linear and unidirectional models of migration to move beyond a classical and potentially deterministic model of studying migrant trajectories. The authors illustrate how many contemporary migrants come and go, not always being sure how long they will stay in the different stopovers on their trajectories, when they will stop migrating or where they will eventually settle. Because of the temporality of their residence, many of these so-called ‘transmigrants’ are not only faced with the same problems and challenges as other migrants, arriving newly in another country and rebuilding social networks, but are additionally confronted with a number of risks that are related to their mobile lifestyle. Although globalization and the porosity of nation state borders facilitate transmigration, they result in juridical and practical complexities, reflected in transmigrants’ everyday struggles. The authors explore these struggles and the difficulties and opportunities transmigrants encounter when they turn to their (transnational) networks to ask for support. Transmigrants’ social life is not only oriented towards their country of residence, but consists of complex networks beyond boundaries. Through visits, telephone calls and the use of social media, many transmigrants create, sustain and (re)discover transnational as well as local social networks. While many address their transnational networks to partly alleviate their needs, the development of local networks still appears as indispensable.