To cite package 'lfe' in publications use:

Simen Gaure (2011) lfe: Linear Group Fixed Effects. R package version 1.4-731.

Corresponding BibTeX entry:

  @Manual{,
    title = {lfe: Linear Group Fixed Effecst},
    author = {Simen Gaure},
    year = {2011},
    note = {R package version 1.4-731},
  }