To cite pssmooth in publications use:

  Michal Juraska (2019). pssmooth: Flexible and Efficient Evaluation of
  Principal Surrogates/Treatment Effect Modifiers. R package version
  1.0.3.

A BibTeX entry for LaTeX users is

  @Manual{,
    title = {pssmooth: Flexible and Efficient Evaluation of Principal
Surrogates/Treatment Effect Modifiers},
    author = {Michal Juraska},
    year = {2019},
    note = {R package version 1.0.3},
  }