To cite package 'xergm' in publications use:

Leifeld, Philip, Skyler J. Cranmer and Bruce A. Desmarais (2017). xergm. Extensions for Exponential Random Graph Models. R package version 1.8.2.

Corresponding BibTeX entry:

  @Manual{,
    title = {xergm: Extensions for Exponential Random Graph Models},
    author = {Philip Leifeld and Skyler J. Cranmer and Bruce A.
      Desmarais},
    year = {2017},
    note = {R package version 1.8.2},
    url = {https://cran.r-project.org/package=xergm},
  }