[Wien] lapw0 using TB-mBJ potential hangs for slab calculations

[Yoshiyuki Ohtsubo]

Dear Professor Blaha and WIEN users,

I am using WIEN2k_11.1 to calculate the surface electronic structure on
semiconductor (Ge) using TB-mBJ potential.
I have found a problem described below and ask for your assistance or 
advice.
I am using the slab geometry to calculate the surface states. The detailed 
structure is in the attached
case.struct file. (It is a test case to compare the well-known surface band 
structure.)

During the SCF cycle, lapw0 seems to hang: never END after one day, while it 
requires only a few minites
for other exchange and correlation potentials, such as PBE96, with the same 
case.struct file.
I know that the similar trouble has been reported for WIEN10.1 in this 
mailing list.
("LAPW0 hangs in mBJ calculation" Tue Dec 14 23:28:10 CET 2010)
However, I could not find how to fix this problem.

My environment for WIEN2k calculation is below.
 Machine: Linux (CENTOS 5) with intel fortran compiler 10.1.021
 Input files: case.struct file is attached. Other input files are made by 
w2web and I modified
              case.in0/inm for mBJ calculation, according to the userguide.
 The case.grr value is fixed at that obtained from Ge bulk (~1.44) during 
the slab calculation.
 I am not using the lapw0_mpi parallel option.

I have already checked these points.
1.
This problem seems to occur due to some delicate conditions. It occurs after 
tens of iterations of SCF
cycles, and slight change of the conditions can avoid this "hanging".
I confirmed that the problem did not occur with a rewind for a few cycles 
and restart the SCF cycle with
another mixing factor. (However, this cycle also hanged a few tens of cycles 
later...)
2.
In case.dayfile, the messages as written below are shown ten times before 
the hang-up.
The same type of messages also appears even when lapw0 finished without the 
hang-up.
===================
int:rho,tauw,grho,g2rho  9.018537139432929E-003  3.896353988848424E-003
  1.185570127100159E-002  3.336162841227647E-003 tauwrong=
  3.190123470208489E-003
===================  (values change gradually)
3.
I inserted the line "print*, tau,g2rho" in the brj.f file to check these 
values.
The hang-up seems to occur when tau and g2rho are very small.
(for example, ~2.3E-007 and 5.6E-009, respectively, for a case I have 
checked)
4.
In my environment, this hang-up problem occurs only for the slab geometry 
with TB-mBJ potential.
TB-mBJ calculation for TiC and bulk semiconductor crystal (Si and Ge) showed 
no hanging-up in lapw0
and the obtained band structure seems to be correct.
The values tau and g2rho were orders of magnitude larger than those written 
above.

If you required any other information in order for me to get some help, 
please ask me. I would send it.
Thank you very much.

////////////////////////////////////////////
Yoshiyuki Ohtsubo
Ph.D. student,
Department of Chemistry, Graduate School of Science, Kyoto University,
Kyoto 606-8502, Japan
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