To cite Amelia in publications use:

  James Honaker, Gary King, Matthew Blackwell (2011). Amelia II: A
  Program for Missing Data. Journal of Statistical Software, 45(7),
  1-47. URL https://www.jstatsoft.org/v45/i07/.

A BibTeX entry for LaTeX users is

  @Article{,
    title = {{Amelia II}: A Program for Missing Data},
    author = {James Honaker and Gary King and Matthew Blackwell},
    journal = {Journal of Statistical Software},
    year = {2011},
    volume = {45},
    number = {7},
    pages = {1--47},
    doi = {10.18637/jss.v045.i07},
  }