To cite tmbstan in publications use:

  Monnahan CC, Kristensen K (2018). No-U-turn sampling for fast
  Bayesian inference in ADMB and TMB: Introducing the adnuts and
  tmbstan R packages PLoS ONE 13(5): e0197954.
  https://doi.org/10.1371/journal.pone.0197954

A BibTeX entry for LaTeX users is

  @Article{,
    title = {No-U-turn sampling for fast Bayesian inference in ADMB and TMB: Introducing the adnuts and tmbstan R packages},
    author = {Cole Monnahan and Kasper Kristensen},
    journal = {PloS one},
    year = {2018},
    volume = {13},
    number = {5},
    doi = {10.1371/journal.pone.0197954},
  }