modified Becke-Johnson potential (mBJ) for band gaps

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modified Becke-Johnson potential (mBJ) for band gaps

Post by Algerien1970 on Fri 29 May - 18:34

From the userguide :


The modified Becke-Johnson exchange potential + LDA-correlation (Tran and Blaha 2009) allows the calculation of band gaps with an accuracy similar to very expensive GW calculations. It is a local approximation to an atomic ``exact-exchange''-potential and a screening term. This is just a XC-potential, not a XC-energy functional, thus  is taken from LSDA and the forces cannot be used with this option.


We recommend the following steps to perform such calculations:


  • run a regular initialization and scf cycle using LDA or PBE,

  • create case.inm_vresp (cp $WIENROOT/SRC_templates/case.inm_vresp case.inm_vresp.

  • edit case.in0 and set "R2V" option (instead of "NR2V").

  • run one more scf-cycle (use run_lapw -NI -i 1) to generate the required case.vresp* files.

  • ``save'' the LDA (PBE) calculation.

  • edit case.in0 and change the functional to option indxc=28.

  • cp case.in0 case.in0_grr and change indxc in case.in0_grr to 50. This option will calculate the average of over the unit cell. (The presence of case.in0_grr will be detected during the scf-cycle and lapw0 will be called twice, first with the input file case.in0_grr, then with case.in0.)

  • run another scf cycle.



In most cases MSEC1 mixing will lead to convergence problems of the scf cycle. One should switch in case.inm to PRATT mixing, first using a smaller mixing factor (eg. 0.2), later increasing it to 0.50.
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