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] _______________________________________________ Quantum ESPRESSO is supported by MaX (www.max-centre.eu/quantum-espresso) users mailing list [email protected] https://lists.quantum-espresso.org/mailman/listinfo/users
