Core Level Shifts / XPS

[janh]

Hi there,

I intend to calculate XPS core level shifts and have been going thru the manual, this forum and the literature to find out how exactly to do this.

I see that I will need to specify:
ICORELEVEL = 0 / 1 /2 (approx final/ initial /acc. final state)
CLNT = 1,2,3,... according to POSCAR
CLN = 1,2,3... N quantum number
CLL = 1,2,3 (l QN)
CLZ = 1 (number of electrons removed from core)

So my question: Where can I find a good description of the procedures VASP uses or maybe a good HOW-TO?
What is the difference between "approximate and accurate final state models", how are they calculated? I found an article by Olovsson et al (Phys. status solidi_243_2006_2447-2464, Core-Level Shifts in complex metallic systems from first principles) which describes several approaches, but I do not clearly see which VASP method they employed. Is there a good book or review highlighting this topic somewhere?

Does it make sense to increase precision, k-point meshes and/or the PW-cutoff for the core level shift single point calculations? Is there a significant dependence of the core level shifts on supercell size, meshes and cutoffs?

Where exactly do I find the according information in the OUTCAR? What I get is basically only what I attached to the very end of this post.

I guess I will get a core level E(1) for a considered system, which I will have to compare to a corresponding bulk or gas phase species level E(2) by:

CLS = (E(1) - E_Fermi(1)) - (E(2) - E_Fermi(2))

am I right? So in practise I can also calculate surface core level sifts by specifying an according species determined thru the POSCAR?

I would appreciate any information on this topic.
Thanks in advance!
Jan Haubrich


Copy from sample OUTCAR for ICORELEVEL = 1:

>>.......
atomic energy EATOM = 48981.36908475
---------------------------------------------------
free energy TOTEN = -113.33800986 eV

energy without entropy = -113.34437826 energy(sigma->0) = -113.34013266


--------------------------------------------------------------------------------------------------------




the core state eigenenergies are

E-fermi : 0.1302 XC(G=0): -7.9677 alpha+bet : -5.0607
add alpha+bet to get absolut eigen values

k-point 1 : 0.0000 0.0000 0.0000
band No. band energies occupation
1 -8.9999 2.00000
.........
<<

[admin]

please have a look at Köhler and Kresse, PRB 70, 165405 (2004) and the references therein.

As the corelevel shifts are not an officially supported feature of vasp, we do not offer any 'cookbook' how to calculate them.
The atom for which the core level shift has to be calculated has to be given in POSCAR, you are right, otherwise the core electrons of all equivalent atoms (as defined in POSCAR) are excited simultaneuosly.
The energy needed to excite a core electron from the core to a conduction band state is TOTEN(2) - TOTEN(1), hence all parameters which are needed to get accurate total energies have to be well-converged.

[metosa]

Dear Admin.

Are core-levels still not supported by VASP ? For example I can't find reference 11 of "Kohler and Kresse, PRB 70, 165405 (2004)"

Thank you