When you report results obtained using GEMPACK, we ask you to acknowledge this by including a reference to GEMPACK in your paper or report. [This acknowledgement is a condition of all GEMPACK licences.]
For example, please include a sentence or footnote similar to the following:
The results reported here were obtained using the GEMPACK economic modelling software [Horridge et al. (2018)].
and include amongst your references:
Horridge J.M., Jerie M., Mustakinov D. & Schiffmann F. (2018), GEMPACK manual, GEMPACK Software, ISBN 978-1-921654-34-3
Some other papers you could cite are listed here.