Dear Shi Kong,
We have very few data to answer properly to your question. What are the
available experimental data and more specifically:
1/ Do you have the atomic structure (cell param. and atomic positions)
for different pressures or only cell parameters variation with pressure?
2/ In the normal structure how many equivalent sites do you have for
the f-element? 1 or more?
If you have one equivalent position for the f-element in the normal
structure, then in the supercell you have many inequivalent sites for
the f-element.
In other words, during the calculation of the small cell you can easily
converged to metal state because all f-atoms are equivalently occupied.
In contrast, in the supercell you allow to have different electronic
configurations for the f-atoms in inequivalent sites. In such situation,
you should be very careful during the SCF convergency, because you could
have charge oscillations due to the alternative occupation of the
inequivalent f-atoms. In addition, you should need to help the system to
converge towards the global minimum electronic configuration using
such an approach:
- change the smearing method (efmod in case.in2), i.e. use GAUSS for
instance with large eval value at the beginning to 0.05
- reduce progressively eval
But it should also be due to an incorrect model for the high pressure
structure:
- because you do not have enough or accurate experimental data
- because the supercell you have generated exhibits an ordering which
lead to the opening of a band gap.
Regards
Xavier
kongshi a ?crit:
Dear WIEN2k users:
Recently I'm calculatingthe f-electron material under pressure with
LDA+U.There are different results between with normal structure file
and with supercell structure file. The result of normal structure file
with symmetry under pressure is metal. But the supercell structure
under pressure result is insulator.The result of spuercell structure
file in atmospheric pressure is metal. In my opinion the pressure
drive the material to the metal state.
Can anybody tell me what the problem is? Thank you in advance.
shi kong
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