Problem related to Bader Charge Analysis

[jianmin]

We are trying to use the VTST Bader Charge Analysis (BCA) program for the TeO2 crystal. What we want to find out is the complete spatial charge distribution for each atom in the crystal. There are 4 Te and 8 O in the TeO2 unit cell. So in total, we want to know the charge distribution of 4*52+8*8=272 electrons.

Since this calculation may be very time-consuming, we want to treat each element separately, and find out all 52 electrons's spatial distribution in Te and all 8 electrons in O. In other words, we would like to use the BCA software to calculate the full charge distribution around the nucleus, not just the valence electrons. Is this possible? Thanks.

[graeme]

I'm a little puzzled by several aspects of this question. First of all, the BCA will give you a complete partitioning of space into 12 regions. You should include the core electrons for this partitioning, but it is only based upon the charge density -- the total number of electrons is irrelevant to the difficulty of the problem. Second, a TiO2 cell with 12 atoms does not strike me as a difficult problem, and I don't see why there should be any need to treat the elements separately. If you have a charge density file, you can run the code and find the Bader partitioning.

[jianmin]

Thanks a lot for your reply, Prof. Graeme.

In the TeO2 unit cell, there are 4 Te atoms and 8 O atoms. One of my questions would be: Since VASP uses the pseudopotential method, there are only 4*6+8*6=72 electrons in the system (all these 72 electrons are valence eletrons.), not 4*52+8*8=272 eletrons, right? If that is the case, there is no information for core electrons, right?

Also, can we visualize the space distribution of charges by any software?

In the section "Bade Charge Analysis", it says "The Bader volumes can be written and visualized with the VASP Data Viewer, VMD, or a cube file viewer (such as GaussView) for Gaussian cube files." But which files are the files that can be visualized? BvAt00xx.dat files, or AECCARx files?

Thanks.

[graeme]

Look at this page for include core charges in vasp:
http://theory.cm.utexas.edu/bader/vasp.php

You can look at the spatial distribution with software that can load chgcar-like files. The AEC* files will show you the charge densities, the Bv* files will show you the Bader volumes.

[jianmin]

Thanks.
By the way, we want to calculate the X-ray form factor, which is given by the Fourier transform of the total charge distribution. How do we do it by VTST tools?

[graeme]

We do not have a script to do a fourier transform, but it would be easy to make one, particularly if you modify one of our existing scripts which reads the charge density files.