that in bulk, dislocations can lead to a signifi cant decrease in κ in the direction perpendicular to the dislocation line. The widely-used theory of Klemens [ 11 ] accounts for this result with perturbation theory, by including scattering of the phonon states (eigenstates of the harmonic crystal) on the linear and non-linear elastic strain regions localized around the dislocation line. By contrast, in SD NWs and NTs, we encounter the unexplored case of thermal transport along the dislocation line. In this work we combine modern theories based on atomistic simulations in order to understand how the thermal properties of Si NWs and NTs accommodating axial SDs with closed and opened cores might differ from the more studied pristine forms. After computing the SD NW and NT structures with objective molecular dynamics [ 12 ] (MD), we used two main methods, the direct method [ 13 ] and the atomistic Green function (AGF) method [ 14 ] (See simulation section), to reveal an important reduction in κ . This fi nding presents signifi cant interest for nanoscale thermoelectricity. We simulated a set of pristine and SD Si NWs and NTs with cubic diamond structure and hexagonal cross sections. The number of 111 layers L in the cross-section was taken to be 12, 16, 20 and 30, so that the radii of the created NWs ranged from 18.8 A to 47.1 A. Next, from the pristine L = 12 NW we created a set of (L,h) NTs, by systematically removing central atomic layers. We label by h the number of 111 inner layers that have been removed. Finally, in all these structures we introduce SDs with the axis located at the center. We considered minimal Burgers vector of magnitude b = 3.8 A and multiples of it, 2b and 3b. In 1b NWs, the created core structure is the Hornstra core, where all atoms remain fourfold coordinated. SDs twist NWs and NTs. This is the Eshelby twist [ 15 ] γ E , which is well known at the macroscale. The presence of γ E creates challenges for the atomistic simulations as it prevents the applicability of the standard periodic boundary conditions. Here, in order to fi nd optimal morphologies (corresponding to minimum energy) we used objective MD [ 12 ]