To cite nlsem in publications use:

Umbach N, Naumann K, Brandt H, Kelava A (2017). “Fitting Nonlinear Structural Equation Models in R with Package nlsem.” Journal of Statistical Software, 77(7), 1–20. doi:10.18637/jss.v077.i07.

Corresponding BibTeX entry:

  @Article{,
    title = {Fitting Nonlinear Structural Equation Models in {R} with
      Package {nlsem}},
    author = {Nora Umbach and Katharina Naumann and Holger Brandt and
      Augustin Kelava},
    journal = {Journal of Statistical Software},
    year = {2017},
    volume = {77},
    number = {7},
    pages = {1--20},
    doi = {10.18637/jss.v077.i07},
  }