To cite gmm in publications use:

Chaussé P (2010). “Computing Generalized Method of Moments and Generalized Empirical Likelihood with R.” Journal of Statistical Software, 34(11), 1–35. https://www.jstatsoft.org/v34/i11/.

Corresponding BibTeX entry:

  @Article{,
    title = {Computing Generalized Method of Moments and Generalized
      Empirical Likelihood with {R}},
    author = {Pierre Chauss{\'e}},
    journal = {Journal of Statistical Software},
    year = {2010},
    volume = {34},
    number = {11},
    pages = {1--35},
    url = {https://www.jstatsoft.org/v34/i11/},
  }