To cite rpmodel in publications use:

  Stocker et al. (2020). P-model v1.0: An optimality-based light use
  efficiency model for simulating ecosystem gross primary production
  Geosci. Model Dev. 13, 1545–1581, 2020 URL
  https://doi.org/10.5194/gmd-13-1545-2020

A BibTeX entry for LaTeX users is

  @Article{,
    title = {P-model v1.0: An optimality-based light use efficiency model for simulating ecosystem gross primary production},
    author = {Benjamin Stocker and Han Wang and Nicholas Smith and Sandy Harrison and Trevor Keenan and David Sandoval and Tyler Davis and Colin Prentice},
    journal = {Geoscientific Model Development},
    year = {2020},
    volume = {13},
    pages = {1545–1581},
    url = {https://doi.org/10.5194/gmd-13-1545-2020},
    doi = {10.5194/gmd-13-1545-2020},
  }