To cite psychomix in publications use:

Hannah Frick, Carolin Strobl, Friedrich Leisch, Achim Zeileis (2012). Flexible Rasch Mixture Models with Package psychomix. Journal of Statistical Software, 48(7), 1-25. URL http://www.jstatsoft.org/v48/i07/.

Corresponding BibTeX entry:

  @Article{,
    title = {Flexible Rasch Mixture Models with Package {psychomix}},
    author = {Hannah Frick and Carolin Strobl and Friedrich Leisch and
      Achim Zeileis},
    journal = {Journal of Statistical Software},
    year = {2012},
    volume = {48},
    number = {7},
    pages = {1--25},
    url = {http://www.jstatsoft.org/v48/i07/},
  }