different occopts give different qualitative result

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different occopts give different qualitative result

Postby ryne60 » Wed Jan 23, 2019 10:44 am

Dear all,

I've been calculating a system with two slightly different structures, say structures A & B. The first set of calculations using occopt 6 and resulted in the total energy of A (EA) smaller than the total energy of B (EB). However, when I use occopt 7 the results show that EB < EA.

Has anyone experienced this before? Can anyone tell me which occopt is better to use?

Thanks!
ryne60
 
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Re: different occopts give different qualitative result

Postby ebousquet » Fri Jan 25, 2019 1:19 pm

Dear ryne60,
The different occopt values use a different "mathematical" expression to smear the electrons and can thus end into different results for the same tsmear value. What you can do is to check how your system change by varying the tsmear value, this would be more consistent. By using occopt=3 (Fermi-Dirac), you at least know that the tsmear value corresponds to a "physical" temperature (temperature of the electrons) while it does not really has a physical meaning for the other cases.
Best wishes,
Eric
ebousquet
 
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Location: University of Liege, Belgium


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