  We represent an approach to calculate micromagnetic model parameters such as
the tensor of exchange stiffness, Dzyaloshinskii-Moriya interaction (DMI) as
well as spin-wave stiffness. The scheme is based on the fully relativistic
Korringa-Kohn-Rostoker Green function (KKR-GF) technique and can be seen as a
relativistic extension of the work of Lichtenstein {\em et al.} The expression
for $D^{z\alpha}$ elements of DMI differ from the expressions for $D^{x\alpha}$
and $D^{y\alpha}$ elements as the former are derived via second-order
perturbation term of the energy caused by spin-spiral while the latter are
associated with the first-order term. Corresponding numerical results are
compared with those obtained using other schemes reported in the literature.
