  The dislocation core field, which comes in addition to the Volterra elastic
field, is studied for the <111> screw dislocation in alpha-iron. This core
field, evidenced and characterized using ab initio calculations, corresponds to
a biaxial dilatation, which we modeled within the anisotropic linear
elasticity. We show that this core field needs to be considered when extracting
quantitative information from atomistic simulations, such as dislocation core
energies. Finally, we look at how dislocation properties are modified by this
core field, by studying the interaction between two dislocations composing a
dipole, as well as the interaction of a screw dislocation with a carbon atom.
