**Geometries of edge and mixed dislocations in bcc Fe from first-
principles calculations**

MR Fellinger and AMZ Tan and LG Hector and DR Trinkle, PHYSICAL REVIEW MATERIALS, 2, 113605 (2018).

DOI: 10.1103/PhysRevMaterials.2.113605

We use density functional theory (DFT) to compute the core structures of
a(0)/**100**(010) edge, a(0)/**100**(011) edge, a(0)/2**(1) over bar(1) over
bar1**(1 (1) over bar0) edge, and a(0)/2**111**(1 (1) over bar0) 71 degrees
mixed dislocations in body-centered cubic (bcc) Fe. The calculations are
performed using flexible boundary conditions (FBC), which effectively
allow the dislocations to relax as isolated defects by coupling the DFT
core to an infinite harmonic lattice through the lattice Green function
(LGF). We use the LGFs of the dislocated geometries in contrast to most
previous FBC-based dislocation calculations that use the LGF of the bulk
crystal. The dislocation LGFs account for changes in the topology of the
crystal in the core as well as local strain throughout the crystal
lattice. A simple bulklike approximation for the force constants in a
dislocated geometry leads to dislocation LGFs that optimize the core
structures of the a(0)/**100**(010) edge, a(0)/**100**(011) edge, and
a(0)/2**111**(1 (1) over bar0) 71 degrees mixed dislocations. This
approximation fails for the a(0)/2**(1) over bar(1) over bar1** (1 (1)
over bar0) dislocation, however, so in this case we derive the LGF from
more accurate force constants computed using a Gaussian approximation
potential. The standard deviations of the dislocation Nye tensor
distributions quantify the widths of the dislocation cores. The relaxed
cores are compact, and the local magnetic moments on the Fe atoms
closely follow the volumetric strain distributions in the cores. We also
compute the core structures of these dislocations using eight different
classical interatomic potentials, and quantify symmetry differences
between the cores using the Fourier coefficients of their Nye tensor
distributions. Most of the core structures computed using the classical
potentials agree well with the DFT results. The DFT core geometries
provide benchmarking for classical potential studies of work-hardening,
as well as substitutional and interstitial sites for computing solute-
dislocation interactions that serve as inputs for mesoscale models of
solute strengthening and solute diffusion near dislocations.

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