My two cents. Both LDA+U and GGA+U are wrong. That said, for f-/d- systems they are often better than LDA/GGA for some properties. The question you should ask yourself is what property are you trying to measure/predict, and what a-priori information (reference state) do you have that can be used?<div>
<br></div><div>For instance, if I want to calculate a surface energy then I would tune the U to give the most accurate bulk energy treating this as my a-priori information; similarly if I wanted to calculate the elastic behavior of a defect I would tune to the bulk elastic constants. In my opinion this is the only justifiable approach.<br>
<br><div class="gmail_quote">On Fri, Mar 1, 2013 at 12:47 PM, Zsolt Rak <span dir="ltr"><<a href="mailto:zsolt.rak@gmail.com" target="_blank">zsolt.rak@gmail.com</a>></span> wrote:<br><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">
<div>
Dear wien2k users, <br>
<br>
I am calculating the properties of several f-electron compounds. I would like to ask the users' opinion about the volume optimization in an f- or d-electron system: which way is better (or physically justified), with LDA/GGA or with LDA+U/GGA+U? In my opinion,
the LDA+U/GGA+U techniques were developed to correct band energies of localized states, so there is no fundamental physical reason to use LDA+U/GGA+U methods for volume optimization. However, we observe a change in the lattice parameters when we go from LDA/GGA
to LDA+U/GGA+U. Also, from a brief search of the literature we found that, in many cases, people tune the Hubbard-U parameter to reproduce the experimental lattice constants.
<br>
I would appreciate further thoughts and insights into this issue.<br>
<br>
Thank you, <br>
Zs
</div>
</blockquote></div><br><br clear="all"><div><br></div>-- <br>Professor Laurence Marks<br>Department of Materials Science and Engineering<br>Northwestern University<br><a href="http://www.numis.northwestern.edu" target="_blank">www.numis.northwestern.edu</a> 1-847-491-3996<br>
"Research is to see what everybody else has seen, and to think what nobody else has thought"<br>Albert Szent-Gyorgi
</div>