To cite package 'xergm' in publications use:

Leifeld, Philip, Skyler J. Cranmer and Bruce A. Desmarais (2016). xergm. Extensions for Exponential Random Graph Models. R package version 1.7.3.

Corresponding BibTeX entry:

  @Manual{,
    title = {xergm: Extensions for Exponential Random Graph Models},
    author = {Philip Leifeld and Skyler J. Cranmer and Bruce A.
      Desmarais},
    year = {2016},
    note = {R package version 1.7.3},
    url = {http://CRAN.R-project.org/package=xergm},
  }