[Wien] a parallel error of lapw0 with MBJLDA potential (updated)

[wanxiang feng]

Dear prof. Blaha

1. I do not fully understand what you mean that "It is probably
completely uncritical for the gap,...".
After the temporary fixed in brj.f, can the code deal with correctly
the system which have very heavy elements?
 and their bandgaps are reasonable?


2. We doubt that there are still some bugs in lapw0_mpi, because the
bandgap is different,

Ge:
0.85eV  (lapw0)
0.71eV  (lapw0_mpi)

GaAs:
1.61eV  (lapw0)
1.37eV  (lapw0_mpi)

Further more, for the first case we provided (test.struct), lapw0_mpi
may lead to unphysical results.
There is a fourfold-degenerate state at about 0.1eV above the fermi
energy from GGA and MBJLDA(using lapw0) results.
This fourfold-degenerate state is protected by symmetry, but it's
absent from MBJLDA result when using lapw0_mpi.


We expect a more reliable version of lapw0 and lapw0_mpi.


Sincerely yours,

Wanxiang Feng



2010/6/11 Peter Blaha <pblaha at theochem.tuwien.ac.at>:
> We will have to make a more detailed analysis.
> Apparently the problem is only near the nucleus for very heavy elements,
> where
> tau or g2rho take values of + or - 10**15 because of diverging subterms.
> It is probably completely uncritical for the gap,...
>
> A temporary fix can be made in brj.f just before the   do while loop
> add the following lines:
>
> tauw = 0.125d0*grho*grho*2.d0/rho
> if(tau.lt.tauw)  tau=tauw
>         D = TAU - 0.25D0*GRHO**2D0/RHO
>         Q = (1D0/6D0)*(G2RHO - 2D0*0.8D0*D)
> if(tau.eq.tauw .and. q.lt.-1.d9)   q=-1.d9   ! eventually experiment with
> the value of q
>
>   10    DO WHILE (DABS(F) .GE. TOL)
>
> We will check if q has some physical bound which could be used as better
> estimate.
>