Electronic and magnetic structure of presumable superconductor BaFe$_2$Se$_3$

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”).