How to locate homo-lumo of a molecule in a composite system?

[askhetan]

Dear All,

I have a molecule that is physisorbed over a surface in a spin polarized system. I want to understand how to locate the homo and lumo levels of this molecule in VASP after performing GW calculations. The fermi level in the OUTCAR file that is used before applying GW corrections is shown as:

The Fermi energy was updated, please check that it is located mid-gap
values below the HOMO (VB) or above the LUMO (CB) will cause erroneous energies
E-fermi : -0.9130

The Fermi energy was updated, please check that it is located mid-gap
values below the HOMO (VB) or above the LUMO (CB) will cause erroneous energies
E-fermi : -0.4668


So from this I get that the final value for Fermi level is -0.4668 eV. (Or are these two values for spin up and down???)However, when I look at the band eigenvalues and occupancies from the valance band and conduction band levels that are written after doing partially self-consistent GW, I see that highest valance band is located in spin up channel at one of the IBZ k-points as:

band No. DFT-energies QP-energies occupation
121 -0.9360 -1.7089 1.0000
122 0.0310 -1.6833 0.0000

and the lowest conduction band is located in the spin down channel at another IBZ kpoint as:

band No. DFT-energies QP-energies occupation
121 -1.1622 -2.3295 1.0000
122 0.8201 -2.1569 0.0000

As you can see from the eigenvalues that the homo-lumo are well below the fermi level assumed by vasp. To get the homo -lumo values of the molecule, I will probably need to plot the partial DOS of the molecule. But the question remains - how can I find out which of its states are occupied and which are empty? The molecule has several states both above and below the fermi level, which by itself is a point of confusion for me because from the band eigenvalues, I see that the lumo (-2.1569) is quite below the fermi-level assigned by vasp. This means there might be molecular states which are unoccupied but still below the fermi level assigned by vasp.

Is there a way to find out the extract the homo and lumo for the molecule from any analysis technique?. Also, My system is metallic with unpaired electrons, with the spin up and spin down channels not showing the same occupancies at different band indexes. Is there as way to count how many electrons are in the spin up and spin down channels from any analysis technique?

Any help is highly appreciated.

[support_vasp]

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