SIGMA

[hongbiao]

In one of the sessions about the oxygen atom, why should SIGMA be reduced when symmetry is lowered?

[Neutrino]

Dear hongbiao,

The oxygen atom is very subtle. Large smear gives you the occupations (which you can check from OUTCAR):

up: 1 1 1 1 0 0
down: 1 0.33 0.33 0.33 0 0


Small smear gives you:

up: 1 1 1 1 0 0
down: 1 1 0 0 0 0


The latter electronic occupation is lower in energy. You will find more discussions about this issue if you search more (forums , published literature, and tutorials).


Mostafa