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Conventional linear elasticity theory predicts the strain fields of a dislocation core to diverge, whereas it is known from atomistic simulations that strains at dislocation cores remain finite. We present an analytical solution to a generalised, variational Peierls-Nabarro model of edge dislocation displacement fields that features a finite core width, as well as the correct isotropic elastic behaviour at large distances away from the core. The strain fields are in qualitative agreement with atomistic simulations of 1 2 [111](121) edge dislocations in bcc tungsten and iron. The treatment is based on the Multi-String Frenkel-Kontorova model that we reformulate as a generalization of the Peierls-Nabarro model using the principle of least action.

Implementation and benchmark of a long-range corrected functional in the density functional based tightbinding method The Journal of Chemical Physics 143, 184107 (2015) To interpret ultrafast dynamics experiments on large molecules, computer simulation is required due to the complex response to the laser field. We present a method capable of efficiently computing the static electronic response of large systems to external electric fields. This is achieved by extending the density-functional tight binding method to include larger basis sets and by multipole expansion of the charge density into electrostatically interacting Gaussian distributions. Polarizabilities for a range of hydrocarbon molecules are computed for a multipole expansion up to quadrupole order, giving excellent agreement with experimental values, with average errors similar to those from density functional theory, but at a small fraction of the cost. We apply the model in conjunction with the polarizable-point-dipoles model to estimate the internal fields in amorphous poly(3-hexylthiophene-2,5-diyl). C 2016 Author(s). All article content, except where otherwise noted, is licensed under a Creative Commons Attribution (CC BY) license