Hello, Sorry if you're getting this message twice, but I'm not sure the first one went through because our department is still in the process of changing email servers.
I have a question about QE's implementation of the the Tersoff-Hamann formalism for simulating STM images. If I understand the stm.f90 code correctly, the energy sampling window does not range from Ef to Ef+sample_bias (which is what Tersoff-Hamann says it should be). Rather, the code increases the upper limit by 3*degauss (degauss=smearing width) and also decreases the lower limit by 3*degauss. In the case of metals, the value of degauss is taken from the prior PW run. I believe the subsequent lines of code modify the weights of the states that are outside the Tersoff-Hamann window. So, as an example, if a metal has a bias of -0.1 eV and the smearing width from the prior PW run was 0.01 Ry (or 0.136 eV), then states from -0.5 eV to +0.4 eV (with respect to Ef) are included in calculating the LDOS. This strikes me as a rather broad range, even if temperature and energy linewidths are considered, and could alter the appearance of the computed images. Why do the STM energy limits take into account the smearing width from the PW output? And is it best to use as small a width as possible if you intend to run STM simulations? Thanks, David Pullman Department of Chemistry and Biochemistry San Diego State University San Diego, CA 92182-1030
