To cite sphet in publications use:

Gianfranco Piras (2010). sphet: Spatial Models with Heteroskedastic Innovations in R. Journal of Statistical Software, 35(1), 1-21. URL http://www.jstatsoft.org/v35/i01/.

Corresponding BibTeX entry:

  @Article{,
    title = {{sphet}: Spatial Models with Heteroskedastic Innovations
      in {R}},
    author = {Gianfranco Piras},
    journal = {Journal of Statistical Software},
    year = {2010},
    volume = {35},
    number = {1},
    pages = {1--21},
    url = {http://www.jstatsoft.org/v35/i01/},
  }