We show that charge ordering (more precisely, two-sublattice bond disproportionation) in the rare earth nickelate perovskites is intimately related to a negative charge transfer energy. By adding an additional potential on the Ni d states we are able to vary the charge tranfer energy and compute relaxed structures within an ab-initio framework. We show that the difference in Ni-O bond lengths and the value of the ordered state magnetic moment correlate with the charge transfer energy and that the transition to the bond-disproportionated state occurs when the effective charge transfer energy becomes negative.
@article{arxiv.1701.06819,
title = {The driving force for charge ordering in rare earth nickelates},
author = {Basudeb Mandal and Sagar Sarkar and Shishir Kumar Pandey and Priya Mahadevan and Cesare Franchini and A. J. Millis and D. D. Sarma},
journal= {arXiv preprint arXiv:1701.06819},
year = {2017}
}