To cite sandwich in publications use:

  Zeileis A, Köll S, Graham N (2020). “Various Versatile Variances: An
  Object-Oriented Implementation of Clustered Covariances in R.”
  _Journal of Statistical Software_, *95*(1), 1-36.
  doi:10.18637/jss.v095.i01 <https://doi.org/10.18637/jss.v095.i01>.

A BibTeX entry for LaTeX users is

  @Article{,
    title = {Various Versatile Variances: An Object-Oriented Implementation of Clustered Covariances in {R}},
    author = {Achim Zeileis and Susanne K\"oll and Nathaniel Graham},
    journal = {Journal of Statistical Software},
    year = {2020},
    volume = {95},
    number = {1},
    pages = {1--36},
    doi = {10.18637/jss.v095.i01},
  }

If sandwich is applied to lm() models, please also cite:

  Zeileis A (2004). “Econometric Computing with HC and HAC Covariance
  Matrix Estimators.” _Journal of Statistical Software_, *11*(10),
  1-17. doi:10.18637/jss.v011.i10
  <https://doi.org/10.18637/jss.v011.i10>.

A BibTeX entry for LaTeX users is

  @Article{,
    title = {Econometric Computing with {HC} and {HAC} Covariance Matrix Estimators},
    author = {Achim Zeileis},
    journal = {Journal of Statistical Software},
    year = {2004},
    volume = {11},
    number = {10},
    pages = {1--17},
    doi = {10.18637/jss.v011.i10},
  }

If sandwich is applied to models other than lm(), please also cite:

  Zeileis A (2006). “Object-Oriented Computation of Sandwich
  Estimators.” _Journal of Statistical Software_, *16*(9), 1-16.
  doi:10.18637/jss.v016.i09 <https://doi.org/10.18637/jss.v016.i09>.

A BibTeX entry for LaTeX users is

  @Article{,
    title = {Object-Oriented Computation of Sandwich Estimators},
    author = {Achim Zeileis},
    journal = {Journal of Statistical Software},
    year = {2006},
    volume = {16},
    number = {9},
    pages = {1--16},
    doi = {10.18637/jss.v016.i09},
  }