Positive energy for the case of METAGGA calculations

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chandan_kumarvishwakarma1
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Positive energy for the case of METAGGA calculations

#1 Post by chandan_kumarvishwakarma1 » Fri May 27, 2022 11:55 am

Dear Users,

I am trying to run scf calculations using METAGGA functional, but in the output file code is printing positive energy.
I am not able to rectify the problem. Please help me regarding the same.

I am attaching all the inputs and few outputs (OSZICAR and OUTCAR), Please find the attachment.

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Regards
Chandan
IIT Delhi, India
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martin.schlipf
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Re: Positive energy for the case of METAGGA calculations

#2 Post by martin.schlipf » Fri May 27, 2022 12:47 pm

You are using the MBJ functional which is not suitable for total energy calculations.
VaspWiki wrote:The MBJ functional is a potential-only functional, i.e., there is no corresponding MBJ exchange-correlation energy, instead E_xc is taken from LDA. This means that MBJ calculations can never be self-consistent with respect to the total energy, and thus we cannot compute Hellmann-Feynman forces (i.e., no ionic relaxation, etc.). Actually, MBJ calculations aim solely at a description of the electronic properties, primarily band gaps. (source)

chandan_kumarvishwakarma1
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Re: Positive energy for the case of METAGGA calculations

#3 Post by chandan_kumarvishwakarma1 » Fri May 27, 2022 1:41 pm

Dear Martin,

Thanks for very prompt reply, I want to mention one point that I am not using MBJ for energy calculations.
I am using this for electronic properties but in between I came to know that in OSZICAR file positive energy is printing.
This was strange for me so I raise this question.

If you can comment more on that then it will be helpful for me.

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Thanks
Chandan

martin.schlipf
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Re: Positive energy for the case of METAGGA calculations

#4 Post by martin.schlipf » Sat May 28, 2022 8:36 am

Use the MBJ functional to get better band structures. It modifies the potential to open the gap compared to local DFT.
However the change to the potential also affects the total energy so it cannot be used to compare structures or for relaxations anymore. The only reason to still print it is to judge whether your electronic structure is converged.

chandan_kumarvishwakarma1
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Re: Positive energy for the case of METAGGA calculations

#5 Post by chandan_kumarvishwakarma1 » Thu Jun 02, 2022 1:59 pm

Dear Martin,
Thanks for your suggestion and clarifications.

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Regards
Chandan

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