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Non-collinear spin density functional theory calculations were employed to study structural, magnetic, and electronic properties of the hexagonal LuMnO3 compound in its ferroelectric phase. For that purpose, it was utilized full-potential linearized augmented plane wave plus local orbitals method, for the first time. The exchange and correlation effects were treated in the frame of the local spin density approximation (LSDA) including effective Hubbard (Ueff) correction. The principal objective of the work was to determine three properties of the LuMnO3 ground state: (1) the crystallographic space group (P63cm or P63), (2) the non-collinear magnetic configuration of the Mn spin moments (Γ1, Γ2, Γ3, Γ4, Γ1 + Γ2 or Γ3 + Γ4), and (3) the electronic structure. The results reveal that the P63cm structure with the Γ3 + Γ4 spin configuration (with ϕ = 80°) should be the ground state. The calculated indirect bandgap of 1.19 eV agrees well with the gap determined from optical conductivity measurements. Analysis of the details of the calculated electronic structure made it possible to interpret the origin of the most pronounced 1.7 eV peak in the optical conductivity spectrum, as well as to explain why it is registered only for the incident light polarized perpendicularly to the c-axis.

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