To cite Rmpi in a publication use:

Yu, H. (2002). Rmpi: Parallel Statistical Computing in R. R News 2/2:10-14.

Corresponding BibTeX entry:

  @Article{,
    title = {Rmpi: Parallel Statistical Computing in R},
    author = {Hao Yu},
    journal = {R News},
    year = {2002},
    volume = {2},
    number = {2},
    pages = {10--14},
    url = {http://cran.r-project.org/doc/Rnews/Rnews_2002-2.pdf},
  }