  The influence of the stress state on the cross-slip rate in Al was analyzed
by means of molecular dynamics simulations and transition state theory. The
activation energy barrier in the absence of thermal energy was determined
through the nudged elastic band method while the cross-slip rates were
determined using molecular dynamics simulations for different magnitudes of the
Schmid stress on the cross-slip plane, and of the Escaig stresses on the
cross-slip and glide planes. The enthalpy barrier and the effective attempt
frequency were determined from the average rates of cross-slip obtained from
the molecular dynamics simulations. It was found that the different stress
states influence the cross-slip rate assuming harmonic transition state theory.
Moreover, the theoretical contributions to the enthalpy barrier
(configurational and due to the interaction of the applied stress with the
local stress field created by the defect) were identified from the atomistic
simulations while the entropic contribution to the activation energy could be
estimated by the Meyer-Neldel rule. Based on these results, an analytical
expression of the activation enthalpy for cross-slip in Al as a function of the
different combinations of Schmid and Escaig stress states was developed and
validated. This expression can be easily used in dislocation dynamics
simulations to evaluate the probability of cross-slip of screw dislocation
segments.
