[Pw_forum] about relax in electric field

[Lorenzo Paulatto]

Replying to message "[Pw_forum] about relax in electric field" from  
Q.J.Wang (24/11/09):
>  PAY ATTENTION: EL FIELD AND OCCUPATIONS

Dear Q.J. Wang,
this message is not very explicative, but it means that Berry-phase  
electric field is not really well defined with smearing and can cause  
problems. In particular, it is not defined for metals, or any system that  
have fractional band occupations.

If you have a band gap and your smearing is much smaller than that, then  
dipfield may work, but if some fractional occupation arises, the system  
may never converge, or converge to some meaningless state.

In practice, if your system has a band gap, albeit small, you should try  
to use fixed occupations. Otherwise, you cannot use dipfield.

best regards

-- 
Lorenzo Paulatto
SISSA  &  DEMOCRITOS (Trieste)
phone: +39 040 3787 511
skype: paulatz
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