To cite package 'GPArotation' in publications use:

Bernaards CA, I.Jennrich R (2005). “Gradient Projection Algorithms and Software for Arbitrary Rotation Criteria in Factor Analysis.” Educational and Psychological Measurement, 65, 676–696.

Corresponding BibTeX entry:

  @Article{,
    author = {Coen A. Bernaards and Robert I.Jennrich},
    year = {2005},
    title = {Gradient Projection Algorithms and Software for Arbitrary
      Rotation Criteria in Factor Analysis},
    journal = {Educational and Psychological Measurement},
    volume = {65},
    pages = {676--696},
  }