To cite sandwich in publications use:

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.

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.

If clustered covariances are used, please also cite:

Berger S, Graham N, Zeileis A (2017). “Various Versatile Variances: An Object-Oriented Implementation of Clustered Covariances in R.” Technical Report 2017-12, Working Papers in Economics and Statistics, Research Platform Empirical and Experimental Economics, Universität Innsbruck. http://EconPapers.RePEc.org/RePEc:inn:wpaper:2017-12.

Corresponding BibTeX entries:

  @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},
  }

  @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},
  }

  @TechReport{,
    title = {Various Versatile Variances: An Object-Oriented
      Implementation of Clustered Covariances in {R}},
    author = {Susanne Berger and Nathaniel Graham and Achim Zeileis},
    institution = {Working Papers in Economics and Statistics, Research
      Platform Empirical and Experimental Economics, Universit\"at
      Innsbruck},
    year = {2017},
    type = {Working Paper},
    number = {2017-12},
    month = {July},
    url = {http://EconPapers.RePEc.org/RePEc:inn:wpaper:2017-12},
  }