  For iridates with large spatially extended 5d orbitals, it may be anticipated
that distant neighbor interactions would play a crucial role in their ground
state properties. From this perspective, we investigate the magnetic structure
of Sr2IrO4 by including interactions beyond first and second neighbors, via
super cell modeling. Adopting to first-principles scalar relativistic methods,
it is found that the minimum in total energy among various magnetic structures
correspond to a up-up-down-down type antiferromagnetic ordering of the Ir ions
for which the magnitude of the electronic gap, that of the Ir local moments
and, the facsimile of the two-peaked structure in the optical conductivity
spectra of Sr2IrO4 were found to be in good agreement with the experiments. The
results unequivocally evidence that the origin of the electronic gap in Sr2IrO4
is due to an unconventional antiferromagnetic ordering of Ir ions, thereby
classifying the system as a Slater magnet, rather than the spin-orbit coupling
driven Jeff = 1/2 Mott insulator.
