Multiwfn forum / gradient of ESP

Re: gradient of ESP

dummy@example.com (sobereva) — Tue, 29 Jul 2025 04:51:59 +0000

I fully understand your situation. I just updated Multiwfn 3.8(dev) on the official website, now you can choose "13 Invert gradient vectors" in post-processing menu to invert the arrows on gradient lines.

BTW: Your image is very nice

Re: gradient of ESP

dummy@example.com (Dirk) — Tue, 29 Jul 2025 04:07:27 +0000

Hello again,
I am plotting 2D ESP maps of a molecule, derived from a wfn file.

The succession in menu numbers is 4 - 12 - 6 which creates an ESP map overlaid by gradient lines that can display
directional arrowheads on the gradient line (which currently point to the opposite direction of the e-field vectors).
In the additional setting I have enabled filling the area between the ESP contour lines with colors and the color index is
then mapped to a scale bar on the right side of the plot. Please have a look at the image of a LiF molecule.

Re: gradient of ESP

dummy@example.com (sobereva) — Tue, 29 Jul 2025 00:14:15 +0000

I don't know what kind of map you plotted. Contour line + gradient line map doesn't have a scale bar.

Re: gradient of ESP

dummy@example.com (Dirk) — Mon, 28 Jul 2025 15:38:04 +0000

This does not help because the scale bar for ESP values would still show the wrong (=inverted) values.
I think for the vector field calculation you are offering the possibility to change the direction of the vectors
to align with the e-field. So the functionality is already present and probably only needs to be enabled for
the direction of the gradient lines ?

Re: gradient of ESP

dummy@example.com (sobereva) — Mon, 28 Jul 2025 14:48:34 +0000

If you are plotting "Gradient lines map with/without contour lines", you can multiply the ESP data by -1 so that the direction of arrows corresponds to electric field, and meantime changing plotting setting of contour lines to exchange solid and dashed styles.

Re: gradient of ESP

dummy@example.com (Dirk) — Mon, 28 Jul 2025 13:59:36 +0000

Dear Tian,

thank you for the fast reply. Well, I tried your suggestion, but the multilication also reverses the values for the ESP and accordingly
produces the wrong charge distribution on the molecule. I think that the option has to work on the gadient calculation only.
The electric field (E) is the *negative* gradient of the electric potential (V): E = -∇V.

Best wishes, Dirk

Re: gradient of ESP

dummy@example.com (sobereva) — Sun, 27 Jul 2025 11:02:57 +0000

Dear Dirk,

This doesn't need a new option. Just select option "-7 Multiply the current data by a factor" in the post-processing menu, and then input -1. Then if you plot the map again by option -1, you will find the arrow direction has been reversed.

Best,

Tian

gradient of ESP

dummy@example.com (Dirk) — Sun, 27 Jul 2025 09:49:55 +0000

Hello Tian,

when analyzing *.wfn files and plotting ESP maps there is an option for plotting also the gradient lines for the ESP.
Unfortunately, the direction of the tips on the gradient lines cannot be changed (=reversed).
At present they point from negative to positive values, whereas e-field lines should point to the opposite direction.
Could you please add an option for changing the direction of the tips ?

Thank you !

Best wishes, Dirk