To cite Ifpack2, please use the following bibliography entry.
@techreport{Ifpack2,
title={Ifpack2 {U}ser’s {G}uide 1.0},
author={Andrey Prokopenko and Christopher M. Siefert and Jonathan J. Hu and Mark Hoemmen and Alicia Klinvex},
number={SAND2016-5338},
year={2016},
institution = {Sandia National Labs},
}