  The influence of magnetism on the properties of screw dislocations in
body-centered cubic chromium is investigated by means of ab initio
calculations. Screw dislocations having Burgers vectors 1/2 111 and 100 are
considered, following experimental observations showing activity for both slip
systems. At low temperature, chromium has a magnetic order close to
antiferromagnetism along 100 directions, for which 1/2 111 is not a periodicity
vector. Hence, dislocations with Burgers vectors 1/2 111 generate magnetic
faults when shearing the crystal, which constrain them to coexist and move
pairwise, leading to dissociated 111 super-dislocations. On the other side, 100
is a periodicity vector of the magnetic order of chromium, and no such magnetic
fault are generated when 100 dislocations glide. Dislocation properties are
computed in the magnetically ordered and non magnetic phases of chromium for
comparison purposes. We report a marginal impact of magnetism on the structural
properties and energies of dislocations for both slip systems. The Peierls
energy barrier opposing dislocation glide in {110} planes is comparable for
both 1/2 111 {110} and 100 {110} slip systems, with lower Peierls stresses in
the magnetically ordered phase of chromium.
