Omitted KPFM approximations

Overview

The KPFM (Kelvin Probe Force Microscopy) flags and key-words in the old ppafm/Master part are only models, that were developed through QMKPFM project. They are based on the equation (1) of L. Gross et al. AFM and KPFM contrast PRB paper. It is also explained in this video poster starting from 0:40.

This work IS NOT connected with Probe-Particle Model related KPFM technique published in SCIENCE 374, pp. 863-867 (2021).

Key Words

The key-words are connected only with the z-component of electrostatic field above the sample as suggested in the PRB paper and so, if you are considering the far-away scans, where your probe-particle is not relaxing, it should accurately capture the KPFM signal, but the exact point of measurements (last PP/last metal atom/C in case of CO?) is still unknown. There are 3 connected key-words in params.ini file, connected with this possible source of KPFM:

KPFM which allows for a calculation of the z-component of electrostatic field and it has four different parameters:

'None'/True - Don't/do calculate the z-component

0.71 - sigma (FWHM) for the gaussian cloud for the density (as in classical electrostatic as explained in Wiki main page) - normally 0.7 or 0.71

0.0 - the z shift with regards, to the final metal atom of the tip-base

1.0 - just a rescale constant (no one knows... ).
KPFM_O - Yes/No - calculate the z-component of electrostatic field in the position of probe particle (PP).
KPFM_C - whether to calculate the z-component of electrostatic field of imaginary second PP (C in case of CO), it has 2 parameters:

Yes/No

1.0 - then rescale between PP - (second PP) - Metal: if 1.0 - same angle as PP; if 0.0 - right under metal.

Running

The KPFM suggestions/approximations, and therefore associated key-words and flags are important during these runs:

generateElFF.py
relaxed_scan.py
plot_results.py : This script is always connected with flags.

Anyway, do not forget to create your LJ potential for the later 2 runs...

Flags

For plotting the results, do not forget to use: --KPFM to plot the results connected with the z-component of electrostatic field. Optionally, you can also plot --totalKPFM flag, for summing the contributions from all important sights - PP, last metallic-tip-atom and imaginary second PP (if specified).

During the run of relaxed_scan.py you can also add flag --tipKPFM Mz, where Mz is the z of the sample highest metallic layer (just for rescale). For plotting these results use: plot_results.py --tipKPFM . This possible contributions is based on differences of z position of PP - as explained in this video poster (starting at 1:40).

Finally, the results are plotted with strange colour scales, since their exact interpretation is not clear at the moment.