To cite gmm in publications use:

  Chausse P (2010). “Computing Generalized Method of Moments and
  Generalized Empirical Likelihood with R.” _Journal of Statistical
  Software_, *34*(11), 1-35. doi:10.18637/jss.v034.i11
  <https://doi.org/10.18637/jss.v034.i11>.

A BibTeX entry for LaTeX users is

  @Article{,
    title = {Computing Generalized Method of Moments and Generalized Empirical Likelihood with {R}},
    author = {Pierre Chausse},
    journal = {Journal of Statistical Software},
    year = {2010},
    volume = {34},
    number = {11},
    pages = {1--35},
    doi = {10.18637/jss.v034.i11},
  }