Charge Density Difference Plots - Trebonius91/utils4VASP GitHub Wiki

The realignment of electron density upon combination of two systems can be analyzed by charge density difference plots. Usual example would be the adsorption of a molecule on a surface. The region and the nature of the bonding can be quantified by such a plot in this case.

First, charge densities (CHGCAR files) of thee systems need to be calculated:

• Full system
• Only surface without adsorbate
• Only adsorbate without surface

All three calculations are simple single point calculations, the locations of the atoms of the respective parts must be exactly the same in the full system and in the surface/adsorbate system! To the INCAR file, add the printout of the CHGCAR file:

• LCHARG = .true.

After finishing the calculation, open VESTA (visit homepage) and then open the CHGCAR file of the full system via the open option in the program.

Then, go to Edit -> Edit Data -> Volumetric Data. There, import the CHGCAR files of both separate systems and click on subtract from current data.

If you want to modify the color of the isosurfaces, go to Objects -> Properties -> Isosurfaces... -> color. There, the typical blue/red orbital picture appearance (red: lower density than isolated systems, blue: higher density than isolated systems) can be obtained by setting the color to 0/0/255. Further, the isosurface-level could be changed (lower value: larger volume captured by the isosurfaces) and the opacity of the isosurfaces can be changed to make the atoms below it more visible.

The resulting isosurface image can be rendered by : File -> Export -> Raster Image.