To cite robustlmm in publications use:

Manuel Koller (2016). robustlmm: An R Package for Robust Estimation of Linear Mixed-Effects Models. Journal of Statistical Software, 75(6), 1-24.<doi:10.18637/jss.v075.i06>

Corresponding BibTeX entry:

  @Article{,
    title = {{robustlmm}: An {R} Package for Robust Estimation of
      Linear Mixed-Effects Models},
    author = {Manuel Koller},
    journal = {Journal of Statistical Software},
    year = {2016},
    volume = {75},
    number = {6},
    pages = {1--24},
    doi = {10.18637/jss.v075.i06},
  }