[Pw_forum] Generating pseudo of Mg with ld1: how to deal with unbound states?

[merlin meheut]

Hi Paolo,

> there is no such thing as an "O-sesame webpage"

Sorry, I have confounded with the Atom "README" file that I found on  
your weppage actually:
http://www.fisica.uniud.it/~giannozz/Atom/README

> nothing is more permanent than "temporary" changes. It was
> "temporarily removed" no less than 5 years ago. It isn't easy
> to generate pseudotentials, the core correction is implemented
> in a lousy way, and a simple analytical form for PP isn't any
> longer as important as it used to be

I followed your advice, and tried to make the pseudos otherwise.  
Actually, my main problem is how to deal with the 3d unbound states in  
Mg. I want to try the different recipies you propose to accomodate  
unbound states on your "Notes on Pseudopotential generation",  
beginning with the third one: "generate PP's on unbound states". There  
are several things concerning that procedure that I would like to  
understand.

My first question is: is that procedure corresponding to the Hamann's  
scheme? If it is, how do you choose the outermost matching radius for  
the 3d orbital?
I do not see a flag corresponding to it. A second, not very important  
question is : is that possible to plot the corresponding unbound 3d  
orbitals? Such as in fig.1 of Fuchs and Scheffler 1999 (Comput. Phys.  
Comm. 119 p67)?

My third and principal question is: how do you choose the "reference  
energy". If it is corresponding to the Hamann's scheme, such as  
implemented in fhi,
Fuchs and Scheffer 1999 state:
"The value of eps_l should be chosen in the energy range where the  
valence states are expected to form bands or molecular orbitals, as a  
default, the program psgen employs the highest eigenvalue of the  
occupied states, e.g., for Al to eps_l = eps_3p"

This seems reasonable, so if I understood well (which I am really not  
sure), for Al, in PBE, eps_l = eps_3p ~ -0.20Ry .
Would it be correct to take a -0.20Ry value for eps_l? It is strange  
to take a negative energy for an unbound state, so maybe I have to  
take +0.20Ry?

This would correspond to the reference energy taken for the Al pseudo  
in /atomic_doc/pseudo-gen/al.in, which is +0.15Ry.

Is that the case? Are these two energies (eps_l and the "reference energy")
the same thing? Or the opposite?

In the case of Mg, 3s2 is -0.44Ry, whereas 3p0 is -0.24Ry. Since 3p is  
empty, the reference energy to take should be around -0.4Ry? +0.4Ry?

Does that make sense?

Thanks again for any hints,

Best regards,

Merlin

Merlin Meheut
Earth and Space Sciences Dept.
University of California at Los Angeles
USA





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