[Wien] Is it really important to use LDA+U on Hg?

[Trond.Brudevoll@ffi.no]

That depends on what you want to achieve. LDA+U can be used for correcting the band structure, but should not be used for volume optimization. If you pull down the Hg 5d states in HgTe by adjusting U until the d-levels approach experimentally observed positions, the ordering of the gamma 6 and gamma 7 levels will be reversed.

 

In the paper you describe, this possibility is mentioned in section IV " .....it is quite plausible that such corrections could alter the order of these levels ....."

 

Now, having put the d-levels in a correct position, you will encounter another problem. The distance between the gamma 8 valence band edge and the gamma 6 band (former conduction band) is known by experiment, so if you are particularly interested in this upper energy region, you could adjust U until this distance coincides with experiments. But this can put the d-levels slightly off their observed experimental position, so it is always a compromise. In some materials it works better than in others ......

 

For discussions on the d-levels you should consult some papers of Van Schilfgaarde:

 

http://www.citebase.org/fulltext?format=application/pdf&identifier=oai:arXiv.org:cond-mat/0111019

 

http://arxiv.org/PS_cache/cond-mat/pdf/0510/0510408.pdf

 

and maybe also:

 

http://theorie.physik.uni-wuerzburg.de/~potthoff/mp/paper/FH05.pdf

 

These papers discuss a GW approach to these problems. The author of the paper you cited does not mention LDA+U, but he mentions GW. And if he had used LDA+U, some of his results would indeed have been different. Fitting with LDA+U can be a "quick fix" when you need it, but be aware that it can have unwanted secondary effects on the shape of other bands too, particularly on DOS. But GW is not without problems either, so I guess that you should use LDA+U here, but use it cautiously.

 

Trond Brudevoll

 

________________________________

Fra: wien-bounces at zeus.theochem.tuwien.ac.at [mailto:wien-bounces at zeus.theochem.tuwien.ac.at] På vegne av Joey Davis
Sendt: 27. juli 2006 10:56
Til: wien at zeus.theochem.tuwien.ac.at
Emne: [Wien] Is it really important to use LDA+U on Hg?

 

Dear all:

I have read some ML about HgTe and HgSe. In HgTe or HgSe, is it really important to use LDA+U on Hg to "pull down" the high lying 5d-electrons?
In PHYSICAL REVIEW B 66, 035117 2002, the auther did not mention to use LDA+U.

when I use LDA+U (I try to do it with different U 0.13 0.26 0.52 Ry )
to calculate HgSe, my 5d-electrons of Hg have been pulled down, but my
DOS is not the same as auther's. When I do not use LDA+U, my DOS is the same as auther's. What should I do, whether or not to use LDA+U.

Thanks in advance and best wishes

   Joey Davis

  

________________________________

Talk is cheap. Use Yahoo! Messenger to make PC-to-Phone calls. Great rates starting at 1¢/min. <http://us.rd.yahoo.com/mail_us/taglines/postman7/*http:/us.rd.yahoo.com/evt=39666/*http:/messenger.yahoo.com> 

-------------- next part --------------
An HTML attachment was scrubbed...
URL: http://zeus.theochem.tuwien.ac.at/pipermail/wien/attachments/20060727/3a72536a/attachment-0001.html