[Wien] Severe bug with MGGA when using Libxc

[Tran, Fabien]

Dear WIEN2k users,

In WIEN2k_21 there is a severe bug when MGGA functionals from Libxc are used (this is a bug in
WIEN2k and not in Libxc).

The self-consistent implementation of MGGA functionals is not yet available in WIEN2k, therefore
a GGA is used for the potential. The problem is that when a Libxc keyword of a MGGA (e.g., SCAN)
in case.in0 is used without specifying the GGA potential:

TOT XC_MGGA_X_SCAN XC_MGGA_C_SCAN (XC_LDA,XC_PBESOL,XC_WC,XC_MBJ,XC_SCAN)

then all results (total energy, band structure, etc.) will be wrong. To obtain the correct results it is
necessary to specify explicitly the GGA (e.g., PBE) potential:

TOT XC_MGGA_X_SCAN XC_MGGA_C_SCAN VX_PBE VC_PBE (XC_LDA,XC_PBESOL,XC_WC,XC_MBJ,XC_SCAN)

Using the original WIEN2k keywords is no problem even when the GGA potential is not specified. Therefore,

TOT XC_SCAN (XC_LDA,XC_PBESOL,XC_WC,XC_MBJ,XC_SCAN)
and
TOT EX_SCAN EC_SCAN VX_PBE VC_PBE (XC_LDA,XC_PBESOL,XC_WC,XC_MBJ,XC_SCAN)

will both produce the correct results.

We will try to provide a bug fix as soon as possible.

FT