[Wien] volume optimization

[Zsolt Rak]

Dear wien2k users,

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.
I would appreciate further thoughts and insights into this issue.

Thank you,
Zs
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