To cite HAC in publications use:

Ostap Okhrin, Alexander Ristig (2014). Hierarchical Archimedean Copulae: The HAC Package. Journal of Statistical Software, 58(4), 1-20. URL http://www.jstatsoft.org/v58/i04/.

Corresponding BibTeX entry:

  @Article{,
    title = {Hierarchical Archimedean Copulae: The {HAC} Package},
    author = {Ostap Okhrin and Alexander Ristig},
    journal = {Journal of Statistical Software},
    year = {2014},
    volume = {58},
    number = {4},
    pages = {1--20},
    url = {http://www.jstatsoft.org/v58/i04/},
  }