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<p class=MsoNormal><font size=2 color=navy face=Arial><span style='font-size:
10.0pt;font-family:Arial;color:navy'>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.<o:p></o:p></span></font></p>
<p class=MsoNormal><font size=2 color=navy face=Arial><span style='font-size:
10.0pt;font-family:Arial;color:navy'><o:p> </o:p></span></font></p>
<p class=MsoNormal><font size=2 color=navy face=Arial><span style='font-size:
10.0pt;font-family:Arial;color:navy'>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 .....”<o:p></o:p></span></font></p>
<p class=MsoNormal><font size=2 color=navy face=Arial><span style='font-size:
10.0pt;font-family:Arial;color:navy'><o:p> </o:p></span></font></p>
<p class=MsoNormal><font size=2 color=navy face=Arial><span style='font-size:
10.0pt;font-family:Arial;color:navy'>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 ......<o:p></o:p></span></font></p>
<p class=MsoNormal><font size=2 color=navy face=Arial><span style='font-size:
10.0pt;font-family:Arial;color:navy'><o:p> </o:p></span></font></p>
<p class=MsoNormal><font size=2 color=navy face=Arial><span style='font-size:
10.0pt;font-family:Arial;color:navy'>For discussions on the d-levels you should
consult some papers of Van Schilfgaarde:<o:p></o:p></span></font></p>
<p class=MsoNormal><font size=2 color=navy face=Arial><span style='font-size:
10.0pt;font-family:Arial;color:navy'><o:p> </o:p></span></font></p>
<p class=MsoNormal><font size=2 face="Courier New"><span style='font-size:10.0pt;
font-family:"Courier New"'><a
href="http://www.citebase.org/fulltext?format=application/pdf&identifier=oai:arXiv.org:cond-mat/0111019">http://www.citebase.org/fulltext?format=application/pdf&identifier=oai:arXiv.org:cond-mat/0111019</a><o:p></o:p></span></font></p>
<p class=MsoNormal><font size=2 face="Courier New"><span style='font-size:10.0pt;
font-family:"Courier New"'><o:p> </o:p></span></font></p>
<p class=MsoNormal><font size=2 color=navy face=Arial><span style='font-size:
10.0pt;font-family:Arial;color:navy'><a
href="http://arxiv.org/PS_cache/cond-mat/pdf/0510/0510408.pdf">http://arxiv.org/PS_cache/cond-mat/pdf/0510/0510408.pdf</a><o:p></o:p></span></font></p>
<p class=MsoNormal><font size=2 color=navy face=Arial><span style='font-size:
10.0pt;font-family:Arial;color:navy'><o:p> </o:p></span></font></p>
<p class=MsoNormal><font size=2 color=navy face=Arial><span style='font-size:
10.0pt;font-family:Arial;color:navy'>and maybe also:<o:p></o:p></span></font></p>
<p class=MsoNormal><font size=2 color=navy face=Arial><span style='font-size:
10.0pt;font-family:Arial;color:navy'><o:p> </o:p></span></font></p>
<p class=MsoNormal><font size=2 color=navy face=Arial><span style='font-size:
10.0pt;font-family:Arial;color:navy'><a
href="http://theorie.physik.uni-wuerzburg.de/~potthoff/mp/paper/FH05.pdf">http://theorie.physik.uni-wuerzburg.de/~potthoff/mp/paper/FH05.pdf</a><o:p></o:p></span></font></p>
<p class=MsoNormal><font size=2 color=navy face=Arial><span style='font-size:
10.0pt;font-family:Arial;color:navy'><o:p> </o:p></span></font></p>
<p class=MsoNormal><font size=2 color=navy face=Arial><span style='font-size:
10.0pt;font-family:Arial;color:navy'>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.<o:p></o:p></span></font></p>
<p class=MsoNormal><font size=2 color=navy face=Arial><span style='font-size:
10.0pt;font-family:Arial;color:navy'><o:p> </o:p></span></font></p>
<p class=MsoNormal><font size=2 color=navy face=Arial><span style='font-size:
10.0pt;font-family:Arial;color:navy'>Trond Brudevoll<o:p></o:p></span></font></p>
<p class=MsoNormal><font size=2 color=navy face=Arial><span style='font-size:
10.0pt;font-family:Arial;color:navy'><o:p> </o:p></span></font></p>
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<p class=MsoNormal><b><font size=2 face=Tahoma><span style='font-size:10.0pt;
font-family:Tahoma;font-weight:bold'>Fra:</span></font></b><font size=2
face=Tahoma><span style='font-size:10.0pt;font-family:Tahoma'> wien-bounces@zeus.theochem.tuwien.ac.at
[mailto:wien-bounces@zeus.theochem.tuwien.ac.at] <b><span style='font-weight:
bold'>På vegne av</span></b> Joey Davis<br>
<b><span style='font-weight:bold'>Sendt:</span></b> 27. juli 2006 10:56<br>
<b><span style='font-weight:bold'>Til:</span></b>
wien@zeus.theochem.tuwien.ac.at<br>
<b><span style='font-weight:bold'>Emne:</span></b> [Wien] Is it really
important to use LDA+U on Hg?</span></font><o:p></o:p></p>
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<p class=MsoNormal><font size=3 face="Times New Roman"><span style='font-size:
12.0pt'><o:p> </o:p></span></font></p>
<p class=MsoNormal style='margin-bottom:12.0pt'><font size=3
face="Times New Roman"><span style='font-size:12.0pt'>Dear all:<br>
<br>
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?<br>
In PHYSICAL REVIEW B 66, 035117 2002, the auther did not mention to use LDA+U.<br>
<br>
when I use LDA+U (I try to do it with different U 0.13 0.26 0.52 Ry )<br>
to calculate HgSe, my 5d-electrons of Hg have been pulled down, but my<br>
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.<br>
<br>
Thanks in advance and best wishes<br>
<br>
Joey Davis<o:p></o:p></span></font></p>
<p><font size=3 face="Times New Roman"><span style='font-size:12.0pt'> <o:p></o:p></span></font></p>
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<p class=MsoNormal><font size=3 face="Times New Roman"><span style='font-size:
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