To cite qqman in publications use:

Stephen D. Turner (2018). qqman: an R package for visualizing GWAS results using Q-Q and manhattan plots. Journal of Open Source Software, 3(25), 731<doi:10.21105/joss.00731>

Corresponding BibTeX entry:

  @Article{,
    title = {qqman: an R package for visualizing GWAS results using Q-Q
      and manhattan plots},
    author = {Stephen Turner},
    journal = {The Journal of Open Source Software},
    year = {2018},
    doi = {10.21105/joss.00731},
  }