A new, simple, computational technique allows molecular electron densities to be divided into atoms which have intuitively correct shapes and charges.

A simple computational technique is introduced for generating atomic electron densities using an iterated stockholder procedure. It is proven that the procedure is always convergent and leads to unique atomic densities. The resulting atomic densities are shown to have chemically intuitive and reasonable charges, and the method is used to analyze the hydrogen bonding in the minimum energy configuration of the water dimer and charge transfer in the borazane molecule.

The interaction of polycyclic aromatic hydrocarbon molecules with hydrogen-terminated graphene is studied using density functional theory with empirical dispersion correction. The effective potential energy surfaces for the interaction of benzene, C(6)H(6), naphthalene, C(10)H(8), coronene, C(24)H(12), and ovalene, C(32)H(14), with hydrogen-terminated graphene are calculated as functions of the molecular displacement along the substrate. The potential energy surfaces are also described analytically using the lowest harmonics of the Fourier expansion. It is shown that inclusion of the dispersive interaction, which is the most important contribution to the binding of these weakly bound systems, does not change the shape of the interaction energy surfaces or the value of the barriers to the motion of polycyclic aromatic hydrocarbon molecules on graphene. The potential energy surfaces are used in the estimation of the friction forces acting on the molecules along the direction of motion. These results underpin the modelling, using density functional theory, of electromechanical devices based on the relative vibrations of graphene layers and telescoping carbon nanotubes.

Common methods of determining atomic polarizabilities suffer from the inclusion of nonlocal effects such as charge polarization. A new method is described for determining fully ab initio atomic polarizabilities based on calculating the response of atomic multipoles to the local electrostatic potential. The localized atomic polarizabilities are then used to calculate induction energies that are compared to ab initio induction energies to test their usefulness in practical applications. These polarizabilities are shown to be an improvement over the corresponding molecular polarizabilities, in terms of both absolute accuracy and the convergence of the multipolar induction series. The transferability of localized polarizabilities for the alkane series is also discussed.

International audienceStatic and dynamic polarizabilities of atoms and functional groups within molecules are calculated from the response of the distributed multipoles to different applied potentials, using a newly developed localisation scheme. The methodology, described here in full for the first time, is based entirely on first-principles calculations. It gives physically reasonable and transferable polarizabilities and dispersion energy coefficients, for multipole components up to at least octopole. Polarizabilities and dispersion energy coefficients determined using this method are used to calculate induction and dispersion energies which are compared with ab initio energies calculated at the Coupled Hartree-Fock level of theory. The localized polarizabilities and dispersion energy coefficients are shown to be an improvement over the corresponding molecular values, in terms of both absolute accuracy as well as convergence properties