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 <[email protected]> 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 <[email protected]>: > > > 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: [email protected] > > -- Postdoctoral Researcher Center for Quantum Nanoscience, Institute for Basic Science Ewha Womans University, Seoul, South Korea
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