[Pw_forum] Semicore states and Spin-orbit coupling

Paul Jennings pcj994 at bham.ac.uk
Wed Feb 23 12:23:52 CET 2011

Dear QE users.

The research group I am in has started to use the QE package but before the group has used AO based codes.
Therefore the concern of my questions is maybe trivial to you. I have two questions and both are connected somehow to
the (ultrasoft)pseudopotentials.

1.) What kind of influence a semicore state in the pseudopotential has on the calculation.  I found some general information of
       the comparison of norm-conserving and non norm-conserving (ultrasoft) pseudopotentials but I don't find any good
       written description of the influence of semicore states. Which properties are altered the
       most if using semicore states and what are the advantages and disadvantages?

2.) Since the systems I have to deal with contain heavy elements the question arises what kind of influence the spin orbit
      coupling has on structural and electronic properties. I found one paper and the two corresponding potentials for gold
      and platinum which incoperate a full relativistic treatment and enable a calculation including spin-orbit coupling for
      the LDA functional. Perhaps I havn't found the example of tutorial but is there a general procedure to incoperate
      SO effects on a GGA or a meta-GGA level yet?

A third question is dealing with the density cutoff.

3.) In the QEwiki is written that a higher density cutoff should be used in the case of ultrasoft pseudopotentials and it should
       be checked that all setting have converged. I have done some calculations and changed first of all the Ecutoff and after
       that the Rhocutoff from four to ten times the Ecutoff. There was no big influence of the Rhocutoff on the structure and energy
       in my particular case. Just to avoid a problem in the future. What properties are altered the most by using a insufficent Rhocutoff?

Best wishes


Paul Jennings

Centre for Hydrogen and Fuel Cell Research
PEMFC Research group
School of Chemical Engineering
The University of Birmingham
Edgbaston, Birmingham B15 2TT (U.K.)

E: PCJ994 at bham.ac.uk
T: 07816644583
W: www.fuelcells.bham.ac.uk


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