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. DOI 10.18637/jss.v058.i04.

A BibTeX entry for LaTeX users is

  @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},
    doi = {10.18637/jss.v058.i04},
  }