[Pw_forum] HUMO and LUMO

[Lorenzo Paulatto]

On Sab, Marzo 28, 2009 20:42, Álvaro Alves wrote:
>  Hello users. How to calculate the HUMO and LUMO in molecular systems in
>  PWscf?

Dear Alvaro,
the definition of homo and lumo only makes sense under certain conditions;
if those conditions are respected pw.x will print homo and lumo energy
just before the total energy, e.g.
  highest occupied, lowest unoccupied level (ev):    -7.4325   -6.2947

I think it only happens if occupation is 'fixed' or from' input. If you're
using a smearing you can still calculate the home and lumo yourself: if
you have only one k-point (gamma) it is not difficult at all.

If you have a small smearing the code shall print the fermi enegy instead
of homo and lumo:
  the Fermi energy is    -4.0615 ev
just after the band energies.
Go up to the bands and look where the fermi energy lies, e.g.
  -20.8969 -10.9562 -10.9562  -5.9557  -0.8632   1.4454   1.4552   1.4553
                         it's here --^
hence -5.9557 is homo and -0.8632 is lumo (as long as the smearing
contribution to energy is ~ zero).

If you are not using gamma as the only kpoint; e.g. you system is not
isolated, than I don't know how much sense it make to compute homo and
lumo (you have a band gap instead), nor how to do it reliably.

cheers

-- 
Lorenzo Paulatto
SISSA  &  DEMOCRITOS (Trieste)
phone: +39 040 3787 511
skype: paulatz
www:   http://people.sissa.it/~paulatto/



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