[QE-users] How to calculate the dI/dV (STS)

[Christoph Wolf]

Dear Thomas,

thank you very much for your detailed explanation, I will try and see how
far I can get with plot_num 3,7 and 10. A lot more options here than
expected ;)

Thanks again and with best regards,
Chris

On Sun, 5 Jan 2020 at 06:07, Dr. Thomas Brumme <thomas.brumme at uni-leipzig.de>
wrote:

> Dear Chris,
>
> within the Tersoff-Hamann approximation the STM image is proportional
> to the integral of the local density of states integrated from the
> Fermi energy till the bias voltage:
>
> https://journals.aps.org/prb/abstract/10.1103/PhysRevB.31.805
>
> As far as I remember, the method implemented in PWscf uses this
> approximation. Accordingly, the STS - which is just dI/dV - should be
> proportional to the local density of states at the bias voltage.
> Two things to remember here:
>
> - STM tips can have apex atoms which have d orbitals and then Tersoff
> Hamann breaks down
> - unoccupied states are - from my experience - hardly ever at the
> correct bias compared to experiments. This is due to the band-gap
> problem but also the curvature (effective mass) can be wrong. Or the
> Fermi energy is at a different position in the experiments. Thus,
> depending on the exchange-correlation functional, agreement for states
> in the unoccupied regime could be false positives...
>
> So, for STM pictures, use the option 5 in pp.x. For STS, either plot
> the closest eigenfunction in real space (option 7) or directly use
> option 3 to plot the local density of states. OR integrate the LDOS
> over a certain region at the specified bias - "simulating" an
> experimental broadening... Option 10.
>
> Hope that helps! Kind regards
>
> Thomas
>
>
> P.S.: Numerical derivative of the STM pictures should also work and
> I also used this about 10 years ago during my Diploma :)
>
>
> Zitat von Christoph Wolf <wolf.christoph at qns.science>:
>
> > Dear all,
> >
> > I was wondering if there is a tool that is able to calculate the dI/dV
> for
> > output from PWSCF? I guess the way it is currently implemented would be
> to
> > calculate a set of STM images for different biases and then take the
> > numerical derivative but for larger systems this is actually really time
> > consuming and since we have the wave functions at the end of a
> calculation
> > there might be a better way to do this. There is for example this code:
> > https://github.com/qphensurf/STMpw which unfortunately is currently not
> > interfaced with PWSCF.
> >
> > Any help is much appreciated!
> >
> > Happy new year everyone!
> >
> > Chris
> >
> > --
> > Postdoctoral Researcher
> > Center for Quantum Nanoscience, Institute for Basic Science
> > Ewha Womans University, Seoul, South Korea
>
>
> --
> Dr. rer. nat. Thomas Brumme
> Wilhelm-Ostwald-Institute for Physical and Theoretical Chemistry
> Leipzig University
> Phillipp-Rosenthal-Strasse 31
> 04103 Leipzig
> Tel: +49 (0)341 97 36456
> email: thomas.brumme at uni-leipzig.de
>
>

-- 
Postdoctoral Researcher
Center for Quantum Nanoscience, Institute for Basic Science
Ewha Womans University, Seoul, South Korea
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