To cite spNNGP in publications use:

Finley AO, Datta A, Banerjee S (2022). “spNNGP R Package for Nearest Neighbor Gaussian Process Models.” Journal of Statistical Software, 103(5), 1–40. doi:10.18637/jss.v103.i05.

Corresponding BibTeX entry:

  @Article{,
    title = {{spNNGP} {R} Package for Nearest Neighbor {G}aussian
      Process Models},
    author = {Andrew O. Finley and Abhirup Datta and Sudipto Banerjee},
    journal = {Journal of Statistical Software},
    year = {2022},
    volume = {103},
    number = {5},
    pages = {1--40},
    doi = {10.18637/jss.v103.i05},
  }