To cite simexaft in publications use:

Wenqing He, Juan Xiong, Grace Y. Yi (2012). SIMEX R Package for Accelerated Failure Time Models with Covariate Measurement Error. Journal of Statistical Software, Code Snippets, 46(1), 1-14. URL http://www.jstatsoft.org/v46/c01/.

Corresponding BibTeX entry:

  @Article{,
    title = {SIMEX {R} Package for Accelerated Failure Time Models with
      Covariate Measurement Error},
    author = {Wenqing He and Juan Xiong and Grace Y. Yi},
    journal = {Journal of Statistical Software, Code Snippets},
    year = {2012},
    volume = {46},
    number = {1},
    pages = {1--14},
    url = {http://www.jstatsoft.org/v46/c01/},
  }