To cite splm in publications use:

Giovanni Millo, Gianfranco Piras (2012). splm: Spatial Panel Data Models in R. Journal of Statistical Software, 47(1), 1-38. URL http://www.jstatsoft.org/v47/i01/.

Corresponding BibTeX entry:

  @Article{,
    title = {{splm}: Spatial Panel Data Models in {R}},
    author = {Giovanni Millo and Gianfranco Piras},
    journal = {Journal of Statistical Software},
    year = {2012},
    volume = {47},
    number = {1},
    pages = {1--38},
    url = {http://www.jstatsoft.org/v47/i01/},
  }