Lcopt has been published in the Journal of Open Source Software.
You can download the citation in BibTeX for use in LaTeX or importing into Mendeley/other reference management software from here.
Or use the following citation:
Joyce, P.J., 2017. Lcopt - An interactive tool for creating fully parameterised Life Cycle Assessment (LCA) foreground models. Journal of Open Source Software, 2:16. doi:10.21105/joss.00339