[QE-users] Full core hole vs Ground state energies

[Pamela Svensson]

I am computing the Binding energies for some C 1s core levels in a molecule, to be compared to an XPS experiment. My problem is related to the core level shift and the ordering of the computed energies (we are not worrying for the absolute values of course but for the relative values).

According to the experiment we have one C 1s XPS peak at 291 eV (Carbon 1) and three very close to each other at about 290 eV (Carbon 2 3 and 4). (in the experiment they express the Binding Energy (BE) as positive, meaning the C1 1s core electron has stronger BE than C2 1s in our case).

The total energies computed for our molecule with quantum espresso with a full core hole in the various carbon atoms are:

core hole in C1 1s= - 263.84140093 Ry (higher)
core hole in C2, 3 and 4 1s ~ -263.89 Ry (lower)

and the ground state (GS) energy for the system is -246.5 Ry (even higher)

(I would expect the GS energy to be lower than the energy of the system with the core hole since I have extracted one electron, but maybe this is only true for a full electron calculation?)

Since we know from the experimental XPS that the binding energy of C1 1s core level is higher than that of C2 1s, why do we get a lower total energy when we perform a core hole in C2 1s than in C1 1s?

In addition, the difference between the GS energy and the total energy with the core hole on C1s is lower than for the core hole in C2, 3 and 4, which is the opposite of what happens in the experiment.

We wonder how we should interpret these total energies in relation to the experimental XPS, and if these total energies we obtain make sense.


Thank you very much!




Pamela Svensson

Uppsala University








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