Аннотация:
We present results of LDA-calculations (band structure, densities of states,
Fermi surfaces) for possible iron based superconductor BaFe$_2$Se$_3$ (Ba123)
in normal (paramagnetic) phase. Results are briefly compared with similar data
on prototype BaFe$_2$As$_2$ and (K,Cs)Fe$_2$Se$_2$ superconductors.
Without doping this system is antiferromagnetic
with $T_{\rm N}^{\exp}\sim250\,$K and rather complicated magnetic structure.
Neutron diffraction experiments indicated the possibility of two possible
spin structures (antiferromagnetically ordered “plaquettes” or “zigzags”),
indistinguishable by neutron scattering. Using LSDA calculated exchange
parameters we estimate Neel temperatures for both spin structures within the
molecular field approximation and show $\tau_1$ (“plaquettes”) spin
configuration to be more favorable than $\tau_2$ (“zigzags”).