I'm a bit confused about the difference between these two concepts. According to Wikipedia the Fermi energy and Fermi level are closely related concepts. From my understanding, the Fermi energy is the highest occupied energy level of a system in absolute zero? Is that correct? Then what's the difference between Fermi energy and Fermi level?


Question: ExPex no longer available
Answer: I contacted the author of ExPex (John Frampton) and he was unaware of the web page issue.  The issue has now been resolved, and the link in the question has been changed (although the link in the question now redirects there). He has no intentions of abandoning development of the package. It is likely that it will be uploaded to CTAN in the future.

Until the package is released on CTAN, users should continue to use this link to get the current version of the package.

Update

ExPex has now been submitted to CTAN, so users should use their package manager or the CTAN website to keep their version up to date.