To cite qgraph in publications use:

  Sacha Epskamp, Angelique O. J. Cramer, Lourens J. Waldorp, Verena D.
  Schmittmann, Denny Borsboom (2012). qgraph: Network Visualizations of
  Relationships in Psychometric Data. Journal of Statistical Software,
  48(4), 1-18. URL http://www.jstatsoft.org/v48/i04/.

A BibTeX entry for LaTeX users is

  @Article{,
    title = {{qgraph}: Network Visualizations of Relationships in Psychometric Data},
    author = {Sacha Epskamp and Ang\'elique O. J. Cramer and Lourens J. Waldorp and Verena D. Schmittmann and Denny Borsboom},
    journal = {Journal of Statistical Software},
    year = {2012},
    volume = {48},
    number = {4},
    pages = {1--18},
  }