To cite ggtern in publications use:

  Hamilton NE, Ferry M (2018). “ggtern: Ternary Diagrams Using
  ggplot2.” _Journal of Statistical Software, Code Snippets_, *87*(3),
  1-17. doi:10.18637/jss.v087.c03
  <https://doi.org/10.18637/jss.v087.c03>.

A BibTeX entry for LaTeX users is

  @Article{,
    title = {{ggtern}: Ternary Diagrams Using {ggplot2}},
    author = {Nicholas E. Hamilton and Michael Ferry},
    journal = {Journal of Statistical Software, Code Snippets},
    year = {2018},
    volume = {87},
    number = {3},
    pages = {1--17},
    doi = {10.18637/jss.v087.c03},
  }