To cite package 'lfe' in publications use:

Simen Gaure (2013) lfe: Linear Group Fixed Effects. R package version 1.4-963.

Corresponding BibTeX entry:

  @Manual{,
    title = {lfe: Linear Group Fixed Effecst},
    author = {Simen Gaure},
    year = {2013},
    note = {R package version 1.4-963},
  }