Abstract: Electronic structure and magnetic structures of BaTi₂Bi₂O are studied with first-principles calculations.In nonmagnetic state,density of states at Fermi level are mostly derived from d_z²,d_x²-y² and d_xy orbitals.Fermi surface (FS) consists of three sheets.The third FS sheet (along X-R line) nests with the first FS sheet (along M-A line) by q-vector q₁=(π/a,0,0) or q₂=(0,π/a,0) shift.Calculated bare susceptibility χ₀(q) peaked at X-point,rather than at M-point in Fe As-based superconductors.Such peaked susceptibility induces spin density wave (SDW).Magnetic ground state is nearly two degenerate antiferromagnetism of bi-collinear antiferromagnetism (AF3) and blocked checkerboard antiferromagnetism (AF4).Peak of susceptibility χ₀(q) is obviously suppressed and becomes slightly in-commensurate with hole doping,but increased with electron doping.As spin fluctuation is suppressed superconductivity appears.It explains that superconductivity appears only in hole-doped compounds,and not in electron-doped ones.

Key words: first-principles calculations, Fermi surface nesting, superconductivity