[QE-users] Error in bandstructure with TB09

[Arini Kar]

Dear all,

I have very recently started using meta-GGA functional and do not have 
much experience with them. I have gone through the previous posts in the 
forum and I understand that selecting an appropriate value of 
c-parameter in TB09 may help in correcting the error in bandstructure 
that I had reported in the previous post. I have upgraded QE version to 
7.0 since it allows to handle external parameters in libxc easily. 
However, I am not able to understand that where and in which script 
should I call the subroutine "set_libxc_ext_param" to change the default 
value of c-parameter, before compiling.

I request you to please guide me through the steps to set the external 
parameters in libxc. Your guidance will be of great help to me in 
proceeding with my work.

Sincerely
Arini Kar
PhD student
Indian Institute of Technology Bombay
India

On 2023-03-22 11:15, Arini Kar via users wrote:

> Dear Quantum Espresso users,
> 
> I am trying to calculate the bandstructure of KCuS using PBE and 
> meta-GGA including SCAN and TB09. I have used norm conserving 
> pseudopotential. The band gap obtained using SCAN is greater than PBE 
> as expected and the topology of the band structure calculated using PBE 
> and SCAN are similar to each other. However, the bandstructure 
> calculated using TB09 is erroneous and very different from that 
> obtained from PBE and SCAN.
> 
> The steps that I have followed for SCAN calculations are as follows:
> 
> * SCF calculation with PBE.
> * SCF calculation with SCAN using wavefunctions of PBE calculation 
> (startingwfc = .true.).
> * NSCF calculation with SCAN along high symmetry k path.
> 
> The steps that I have followed for TB09 calculations are as follows:
> 
> * SCF calculation with PBE.
> * SCF calculation with SCAN using wavefunctions of PBE calculation 
> (startingwfc = .true.).
> * SCF calculation with TB09 using startingpotential from SCAN 
> calculation (startingpot = .true.).
> 
> * NSCF calculation with TB09 along high symmetry k path.
> 
> _In the above, TB09 calculation right after PBE calculation gives rise 
> to convergence issues. As a work around I have performed PBE, SCAN and 
> then TB09 calculations._
> 
> I am using QE v6.8. I have attached the input files and the 
> bandstructure of all these calculations. I request you to help me 
> resolve this error.
> 
> Regards
> Arini Kar
> PhD student
> Indian Institute of Technology Bombay
> India
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