[Wien] electron transfer - RMT spheres

[Gheorghe P]

     Dear Wien users,

     I am studying a system which has a structural transition; above the structural transition all the Co ions are in equivalent positions having an octahedral environment with oxygen ions in the corners of the octahedra (distance Co-O = 1.95); below the structural transition the oxygen ions move such that there will be two inequivalent sites for Co after the distortion; Co1 will be inside a contracted octahedra (Co-O = 1.91) and Co2 will be inside an expanded octahedra (Co-O = 2.02). From some measurements I expect that at the structural transition there is a electron transfer from the Co1 site to the Co2 site; to test this scenario I did an experiment using resonant X-ray scattering at the Co K edge; during the scattering an electron from the 1s level is moved into an empty 4p state (for a very short time); so in my case I will have (for both Co1 and Co2) a shift of the 1s level due to the electron transfer and in the same time I will have a shift
 of the 4p states due to the hybridization of the Co 4p states with O 2p states. 

I would like to calculate these shifts of the 1s and 4p level for both Co1 and Co2 and to obtain a "quantitatively" value for the electron transfer using WIEN2k but i have a question about how to set up the RMT spheres around the Co ions during the calculations.

I read so far in the emailing list (see below) that if I want to obtain a approximate value for the electron transfer I have to look at the charge in the RMT spheres.

My question is about how to set the RMT sphere for the two ions Co1 and Co2????? 

I did a non-magnetic calculation using the w2web interface; if I use the default program from the w2web graphical interface, the calculated spheres for Co1 and Co2 are identical and there is no electron transfer between the two spheres; but in the reality if there is an electron transfer the ionic radius of Co1 and Co2 would be different. 

So how do I have to set up the sphere such that the calculations model as good as possible my system???

Thank you very much in advance for any help you can give me to understand how to model this problem.

Best wishes,
Lucian





++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
Jorissen Kevin 
    Kevin.Jorissen at ua.ac.be
       

    Tue Nov  4 13:43:42 CET 2003
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Some possibilities :
* draw charge density maps and difference density maps
* do Bader analysis
* look at the charges in the MT
Eg. in PRB67 075102 you'll find these three methods
 used and compared (APW calculations of Cu2O).
 
As there is no unambiguous definition of charge transfer,
different methods will yield different quantitative values.
But you can hope to discover trends.
 
Kevin.++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++





      
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