To cite hergm in publications use:

Schweinberger M, Luna P (2018). “hergm: Hierarchical Exponential-Family Random Graph Models.” Journal of Statistical Software, 85(1), 1–39. doi: 10.18637/jss.v085.i01.

Corresponding BibTeX entry:

  @Article{,
    title = {{hergm}: Hierarchical Exponential-Family Random Graph
      Models},
    author = {Michael Schweinberger and Pamela Luna},
    journal = {Journal of Statistical Software},
    year = {2018},
    volume = {85},
    number = {1},
    pages = {1--39},
    doi = {10.18637/jss.v085.i01},
  }