To cite package copula in publications use:

Yan, J. Enjoy the Joy of Copulas: with a Package copula Journal of Statistical Software, 21(4), pp1--21.

Corresponding BibTeX entry:

  @Article{,
    title = {Enjoy the Joy of Copulas: with a Package copula},
    author = {Jun Yan},
    year = {2007},
    journal = {Journal of Statistical Software},
    volume = {21},
    number = {4},
    pages = {1--21},
  }