  Density functional theory calculations have been performed for the
structural, electronic, magnetic and ferroelectric properties of a
mixed-valence Fe(II)-Fe(III) formate framework [NH$_2$(CH$_3$)$_2$][Fe$^{\rm
III}$Fe$^{\rm II}$(HCOO)$_6$] (DMAFeFe). Recent experiments report a
spontaneous electric polarization and our calculations are in agreement with
the reported experimental value. Furthermore, we shed light into the
microscopic mechanism leading to the observed value and as well how to possibly
enhanced the polarization. The interplay between charge ordering, dipolar
ordering of DMA$^+$ cations and the induced structural distortions suggest new
interesting directions to explore in these complex multifunctional hybrid
perovskites.
