[QE-users] Including Spin-orbit coupling only in selected atoms

[Giovanni Cantele]

Dear Lorenzo,

a calculation of this kind should work in principle: to include spin-orbit
effects, at least one atomic species must be described with a fully
relativistic pseudopotential, so using a fully relativistic pseudopotential
for the substrate and a scalar-relativistic one for the overlayer is a
reasonable way to test how much of the effect comes from the overlayer SOC
itself.
That said, if the goal is to make a reliable statement about the physical
origin of the splitting, I would still recommend using fully relativistic
pseudopotentials for all species in the final calculations. In many systems
the enhancement is not due purely to the heavy atom’s intrinsic SOC, nor
purely to symmetry lowering, but to their interplay. The overlayer can
modify the symmetry of the surface or interface and at the same time
hybridize with the surface state, transferring spin-orbit character to it.
A well-known example is graphene/WSe2, where even a relatively weak van der
Waals interaction leads to mixing between graphene pi states and
spin-orbit-active WSe2 states. The interface symmetry then determines which
kind of induced SOC terms can appear, for example Rashba-like terms when
inversion symmetry is broken, and in some systems valley-Zeeman-like terms.
I would also pay attention to the bonding mechanism between the surface and
the overlayer. If the interaction is weak, a proper treatment of van der
Waals forces may be important, since the induced spin-orbit effects can be
very sensitive to interlayer distance and hybridization.

Giovanni
-- 

Prof. Giovanni Cantele
Dipartimento di Fisica "Ettore Pancini"
Universita' degli Studi di Napoli "Federico II"
Complesso Universitario M. S. Angelo - Ed. 6
Via Cintia, I-80126, Napoli, Italy
e-mail: giovanni.cantele at unina.it
Phone: +39 081 676910

Web page: https://sites.google.com/view/giovanni-cantele/home


Il giorno mer 25 mar 2026 alle ore 11:26 Lorenzo Sponza <
lorenzo.sponza at onera.fr> ha scritto:

> Dear Users and Developers,
>
> I am studying the electronic structure of a surface covered by a heavy
> metal overlayer. I have reasons to think that the interaction between the
> two elements enhances the spin-orbit splitting of a particular surface
> state. I would like to understand which is the dominating effect in such an
> enhancement : is it mainly due to symmetry changes induced by the overlayer
> or to the spin-orbit carried by the overlayer's atoms?
>
> To this aim, I'm planning to run a simulation with a full-relativistic
> pseudopotential for the substrate element, and a scalar-relativistic one
> for the overlayer atoms. My questions are (1) Is that a safe procedure,
> i.e. does QE handle such a mixed kind of simulation? (2) Is there any other
> delicate aspects I should be aware of when carrying out a simulation like
> this?
>
> Many thanks in advance. Cheers
> --
> Dr. Lorenzo Sponza
>
> Chargé de Recherche au CNRS
> Université Paris-Saclay, ONERA, CNRS Laboratoire d'étude des
> microstructures (LEM)
> 29 Avenue de la division Leclerc, 92322 Châtillon
> Tel: +33146734464
>
> ETSF Research Team Leader
> European Theoretical Spectroscopy Facility
> https://sites.unimi.it/etsf/
>
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