  We have investigated the crystal, electronic, and magnetic structure of Mn5O8
by means of state of-the-art density functional theory calculations and neutron
powder diffraction (NPD) measurements. This compound stabilizes in the
monoclinic structure with space group C2/m where the Mn ions are in the
distorted octahedral and trigonal prismatic coordination with oxygen atoms. The
calculated structural parameters based on total energy calculations are found
to be in excellent agreement with low temperature NPD measurements when we
accounted correct magnetic structure and Coulomb correlation effect into the
computation. Bond strength analysis based on crystal orbital Hamiltonian
population between constituents indicating strong anisotropy in the bonding
behavior which results in layered nature of its crystal structure. Using fully
relativistic generalized-gradient approximation with Hubbard U (GGA+U) we found
that the magnetic ordering in Mn5O8 is A-type antiferromagnetic and the
direction of easy axis is [1 0 0] in agreement with susceptibility and NPD
measurements. However, the calculation without the inclusion of HubbardU leads
to ferrimagnetic half metal as ground state contradictory to experimental
findings, indicating the presence of strong Coulomb correlation effect in this
material. The GGA calculations without Coulomb correction effect itself is
sufficient to reproduce our experimentally observed magnetic moments in various
Mn sites.
