To cite the mixcat package in publications use:

  Papageorgiou, G. & Hinde, J. (2012) Multivariate generalized linear
  mixed models with semi-nonparametric and smooth nonparametric random
  effects densities. Statistics and Computing, 22, 79--92

A BibTeX entry for LaTeX users is

  @Article{,
    title = {Multivariate generalized linear mixed models with semi-nonparametric and smooth nonparametric random effects densities},
    author = {Georgios Papageorgiou and John Hinde},
    journal = {Statistics and Computing},
    year = {2012},
    volume = {22},
    pages = {79--92},
    doi = {10.1007/s11222-010-9207-y},
    url = {https://doi.org/10.1007/s11222-010-9207-y},
  }