ABINIT Discussion Forums

I cannot understand the ussage of occ variable.

The all variables help file mentioned

Typical band occupancy is either 2 or 0, but can be 1 for half-occupied band or other choices in special circumstances.

Thus, I think that It should be 0 if the band is un-occupied, 1 if the band is half-occupied and 2 if the band is full-occupied. But I saw an input file (https://docs.abinit.org/tests/v3/Input/t19.in) which broke my understanding by 6*1/3. I want to know what one thrid means. Is there are some troubles on my thought?

In a nutshell, could you tell me what OCCupation numbers especially one third means on earth?

Dear skyair,
Although we know that electrons cannot be split, there is no problem mathematically to have fractional occupancies in density functional theory.
Please, have a look at :
- JP Perdew et al, Phys. Rev. Lett 49, 1691 (1982)
- Gross et al Phys Rev A 37, 2809 (1988)
There are many others references about fractional occupations ...
Best