To cite simsurv in publications use:

Brilleman SL, Wolfe R, Moreno-Betancur M, Crowther MJ (2020). “Simulating Survival Data Using the simsurv R Package.” Journal of Statistical Software, 97(3), 1–27. doi: 10.18637/jss.v097.i03.

Corresponding BibTeX entry:

    title = {Simulating Survival Data Using the {simsurv} {R} Package},
    author = {Samuel L. Brilleman and Rory Wolfe and Margarita
      Moreno-Betancur and Michael J. Crowther},
    journal = {Journal of Statistical Software},
    year = {2020},
    volume = {97},
    number = {3},
    pages = {1--27},
    doi = {10.18637/jss.v097.i03},