We apply a full-potential first-principles method to investigate the e
lectronic-structure and elastic features of pure iron and ordered tran
sition metal systems like Fe-Ni and Fe-Mn. The martensitic phase trans
formations in these compounds mainly depend on the properties of iron.
Therefore the phase diagram of iron has been studied in detail in vie
w of structural transformations and magnetic order. To this the total
energy and magnetic moment have been investigated as function of the a
tomic volume. In agreement with experimental results, we find a ferrom
agnetic bcc ground-state and an antiferromagnetic fee phase having a h
igher energy of 7 mRy. The resulting pressure for the bcc --> hcp tran
sition is about 11.5 GPa in agreement with experiments. Besides that,
total energy calculations have been done for stoichiometric Fe-Mn and
Fe-Ni compounds. The resulting alloy phase diagrams are in a good agre
ement with the experimental data.