What is the minimum number of individuals per group required for ADMIXTURE analysis? What is the minimum number of individuals required per group (population/species) for an ADMIXTURE analysis to be appropriate?

Is there a way to determine this number mathematically based on the amount of genetic data I have or other criteria?

Are there any citations I can use to figure this information out?
The following paper provides an in-depth exploration of factors affecting power of admixture analyses under a number of different models. Although the authors state they "provide the open-source R software AdmixPower, to perform power and sample size analysis", in fact it seems the software is not available.

AdmixPower: Statistical Power and Sample Size Estimation for Mapping Genetic Loci in Admixed Populations

Tool availability:

https://research.cchmc.org/mershalab/Tools.html

Site asks for a password, apparently there is no option to sign up.