different occopts give different qualitative result

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ryne60
Posts: 18
Joined: Thu Dec 06, 2018 8:57 am

different occopts give different qualitative result

Post by ryne60 » Wed Jan 23, 2019 9:44 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!

ebousquet
Posts: 313
Joined: Tue Apr 19, 2011 11:13 am
Location: University of Liege, Belgium

Re: different occopts give different qualitative result

Post by ebousquet » Fri Jan 25, 2019 12:19 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

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