  A large number of published experimental works suggest that when the Fe ions
in orthorhombic LaFeO3 are substituted, band gap reduction is expected.
However, recent experimental works observe band gap enhancement with increasing
Ti ions replacing Fe ions. While satisfactory explanation on such observations
seem absent, a first principles investigation may answer what should really
happen. We investigate from first-principles the influence of Ti substitution
on LaFeO3 at Fe-site as a function of substitution concentration. Amongst the
five investigated models, we found that as the Ti substitution concentration
increases, the electronic band gap at Fermi level decreases. However, in the
model where two Ti ions replace Fe sites in an anti-symmetric arrangement, the
Fermi level is crossed. We found that band gap reductions could be caused by
the decreased in field splitting between the Fe 3d orbitals and charge
competition between Fe-O and Ti-O bonds as inferred from density of states
analysis. While band gap reduction with increasing substitution implies better
conductivity, cohesive energy becomes less negative although the perovskite
distortion parameter does not differ significantly between each models.
