To cite lme4 in publications use:
Bates D, Mächler M, Bolker B, Walker S (2015). “Fitting Linear Mixed-Effects Models Using lme4.” Journal of Statistical Software, 67(1), 1–48. doi:10.18637/jss.v067.i01.
Corresponding BibTeX entry:
@Article{, title = {Fitting Linear Mixed-Effects Models Using {lme4}}, author = {Douglas Bates and Martin M{\"a}chler and Ben Bolker and Steve Walker}, journal = {Journal of Statistical Software}, year = {2015}, volume = {67}, number = {1}, pages = {1--48}, doi = {10.18637/jss.v067.i01}, }