  We present a study based on several advanced First-Principles methods, of the
recently synthesized PbNiO3 [J. Am. Chem. Soc 133, 16920 (2011)], a
rhombohedral antiferromagnetic insulator which crystallizes in the highly
distorted R3c crystal structure. We find this compound electrically polarized,
with a very large electric polarization of about 100 (\muC/cm)^2, thus even
exceeding the polarization of well-known BiFeO3. PbNiO3 is a proper
ferroelectric, with polarization driven by large Pb-O polar displacements along
the [111] direction. Contrarily to naive expectations, a definite ionic charge
of 4+ for Pb ion can not be assigned, and in fact the large Pb 6s-O 2p
hybridization drives the ferroelectric distortion through a lone-pair mechanism
similar to that of other Pb- and Bi-based multiferroics

Strongly Correlated Electrons;Materials Science