[QE-users] Error in bandstructure with TB09

[Arini Kar]

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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