Ab initio full-potential study of the structural and magnetic phase stability of iron

We have investigated the magnetic and structural phase diagram of iron empl oying the full potential linear augmented plane-wave method within the gene ralized gradient approximation. Therefore, total-energy calculations have b een performed together with investigations with varying cia ratio to check the phase stability. This study focuses on the structural and magnetic prop erties relevant to Invar and anti-Invar and structural phase transitions oc curring in these materials. We show that the properties of antiferromagneti c fee iron can be understood by collinear full potential calculations. In o rder to do this, the antiferromagnetic structure has been distorted by shor t-range ferromagnetic nearest-neighbor coupling. From this we can conclude that, the classical low-spin behavior can be replaced by antiferromagnetic ordering. Additionally, the thermal properties of iron, especially the free -energy and thermal-expansion coefficient alpha(T) have been analyzed, whic h is important for the understanding of the anti-Invar effect. The free ene rgy and alpha(T) were estimated from a Debye scheme for which nb initio res ults were given as input. Besides the more common cubic phases we have inve stigated hcp Fe at large volumes in view of its magnetic structure. [S0163- 1829(99)07929-1].