To cite mirt in publications use:

  R. Philip Chalmers (2012). mirt: A Multidimensional Item Response
  Theory Package for the R Environment. Journal of Statistical
  Software, 48(6), 1-29. doi:10.18637/jss.v048.i06

A BibTeX entry for LaTeX users is

  @Article{,
    title = {{mirt}: A Multidimensional Item Response Theory Package for the {R} Environment},
    author = {R. Philip Chalmers},
    journal = {Journal of Statistical Software},
    year = {2012},
    volume = {48},
    number = {6},
    pages = {1--29},
    doi = {10.18637/jss.v048.i06},
  }