[xcrysden] question about difference charge density plot

[Tone Kokalj]

On Fri, 2014-03-14 at 23:53 -0700, Romeda Azeen wrote:
> Dear all
> I'm a new user of Wien2k/Q.E. Recently I am trying to analyze the
> difference charge density plots (crystal density minus the superposed
> atomic densities) for Gd5Ge4 compound. I got 2D plot via xcrysden
> utility. But i am troubling to analyze the plots. By using color
> thermo meter what can we conformed?. i.e if the value is
> negative/positive or even zero means what? I want to know the flow
> from where to where? Is it from lower electro negativity element to
> higher electro negativity element? How can we conform the type of
> bonding between them (ionic, covalent and metallic bonding) from these
> plots? 


These are very general questions that go beyond the usage of xcrysden.

For the charge density plots the general recommendation would be the
following:

1. chose a symmetric plotting range, i.e., from -value (Lowest rendered
value) to +value (Highest rendered value). 

2. select the "blue-white-red" colorscale

By performing steps 1+2 the blue color will indicate the electron
deficit regions, red color will indicate the electron access regions
(i.e. electron charge flowed from blue to red), and white color
indicates the zero-difference.

What is the proper choice for the above "value"? You have to find out by
yourself iteratively by xcrysden. Say start from 0.1 and go down
logarithmically (e.g., 0.01, 0.001). You will soon notice what is the
proper order of magnitude, then you may fine-tune the "value".

Regards,
-- 
Anton Kokalj
J. Stefan Institute, Jamova 39, 1000 Ljubljana, Slovenia 
(tel: +386-1-477-3523 // fax:+386-1-477-3822)

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