[gpaw-users] Generating a core-hole setup with generator2

[Mathias Ljungberg]

Hi Toma,


On Mar 20, 2015, at 12:30 PM, Toma Susi wrote:

> A quick comment be Mathias’ reply below.
> 
>> ------------------------------
>> 
>> Message: 2
>> Date: Thu, 19 Mar 2015 21:08:38 +0100
>> From: Mathias Ljungberg <mathias.ljungberg at fysik.su.se>
>> To: Eric Hermes <ehermes at chem.wisc.edu>
>> Cc: gpaw-users <gpaw-users at listserv.fysik.dtu.dk>
>> Subject: Re: [gpaw-users] Generating a core-hole setup with generator2
>> Message-ID: <C01A3F07-2DA6-4E07-A3BA-835CD2C8BE45 at fysik.su.se>
>> Content-Type: text/plain; charset=us-ascii
>> 
>> Hi Eric, 
>> 
>> On Mar 19, 2015, at 7:16 PM, Eric Hermes wrote:
>> 
>>> Hello,
>>> 
>>> I am attempting to generate a setup for Pd with a core hole in the 3d state using generator2. If I generate the setup with '-f PBE -w -s Pd --core-hole 3d,1.0', several new additional bound states appear that did not exist in the ground-state calculation (2 s-states, 2 p-states, and 3 d-states). Here is an example output from this calculation:
>>> https://gist.github.com/ehermes/6c85184e16d43acb6992
>>> 
>>> If I instead generate the setup by specifying the electron configuration with '-C' (as [Ar] 3s2 3p6 3d9 4s2 4p6 4d10 5s1), I receive no error and get what appears to be a working core-hole setup for Pd. In addition, the total all-electron scalar-relativistic energy difference between the ground state and core-hole Pd atom is quite close to the experimental metallic Pd 3d binding energy (334.2 eV vs ~335.2 eV). This indicates to me that this procedure works. However, I am not using the "--core-hole" argument to do this. Is what I am doing valid? Here's the output file from the calculation I have described:
>>> https://gist.github.com/ehermes/3aec73bb427bbc6efe7c
>>> 
>> 
>> I think that both methods create setups with core holes. One difference is that the latter method puts an extra electron in the valence, which perhaps isn't such bad idea. It is true that the first method seems to give larger errors in the grid diagonalization check. There are many more parameters to play with to get these errors small, cutoff radii, energies of projectors etc. 
> 
> Do you really think it’s a good idea to have the extra valence electron already in the setup (as opposed to specifying the charge in the calculator to make the unit cell neutral)?
> 

I assumed that both setups have the core charge of 35 electrons which means they will be charged in the same way. The extra electron, I believe,  will not be visible, it is just a trick to create appropriate projectors etc. I may be wrong though. It would be easy to test it by doing a calculation of the single atom in the grid basis.

Best, 
Mathias



> I guess for metallic systems the end result is the same, but would be interesting if Eric could confirm this.
> 
>> 
>> The --core-hole argument does two things: firstly it corrects the core density when computing the xc potential so that the hole actually sits in one of the spins. This can have the effect of ~10 eV or so in the total energy for molecules. Secondly, it computes some transition dipole matrix elements to be used in XAS, but as far as I know it is only implemented for s-states.  Maybe you could try to set both the occupations to get the extra electron there and use the --core-hole argument for the core hole. In the end of course the setup needs to be tested in a real calculation to judge its quality.
>> 
>> (Also, the total energy differences between the two methods is only 7.5 eV which will be compensated by the valence electrons when putting the setup into a real system.)
>> 
>> Best regards, 
>> Mathias
>> 
>> 
>> 
>>> Also, I understand that the setups used for the ground state Pd and core-excited Pd should be of comparable quality, and that the best way to ensure this is to generate both setups as similarly as possible. However, the default setup parameters for Pd in generator2 do not seem to produce a good quality setup. While the official setups produce lattice constants (3.946 for 10-electron and 3.937 for 18-electron) that are in fairly good agreement with an all-electron FP-LAPW calculation (3.948 angstrom), the default Pd setup generated by generator2 predicts a lattice constant that is more than 0.02 angstrom too large (3.972). If I use the cutoffs from the official 10-electron setup ([2.3, 2.5, 2.2]) instead of generator2's default cutoff (2.4), the lattice constant is in much better agreement (3.958). As I am not an expert in generating pseudopotentials, I wonder what the best procedure here is, and how to best measure the quality of a setup. Any advice would be appreciated.
>>> 
>>> Thank you,
>>> Eric Hermes
>>> 
>>> -- 
>>> Eric Hermes
>>> J.R. Schmidt Group
>>> Chemistry Department
>>> University of Wisconsin - Madison
>>> 
>>> _______________________________________________
>>> gpaw-users mailing list
>>> gpaw-users at listserv.fysik.dtu.dk
>>> https://listserv.fysik.dtu.dk/mailman/listinfo/gpaw-users
>> 
>> 
>> 
>> 
>> ------------------------------
>> 
>> _______________________________________________
>> gpaw-users mailing list
>> gpaw-users at listserv.fysik.dtu.dk
>> https://listserv.fysik.dtu.dk/mailman/listinfo/gpaw-users
>> 
>> End of gpaw-users Digest, Vol 62, Issue 26
>> ******************************************
> 
> 
> _______________________________________________
> gpaw-users mailing list
> gpaw-users at listserv.fysik.dtu.dk
> https://listserv.fysik.dtu.dk/mailman/listinfo/gpaw-users