[Wien] SECLR4 error in large supercells / high number of k points

[Kurt Lejaeghere]

Dear wien2k mailing list users

Considering the question
http://zeus.theochem.tuwien.ac.at/pipermail/wien/2010-March/012785.html
and the answers considered in
http://zeus.theochem.tuwien.ac.at/pipermail/wien/2010-March/012789.html
http://zeus.theochem.tuwien.ac.at/pipermail/wien/2010-April/012795.html
http://zeus.theochem.tuwien.ac.at/pipermail/wien/2010-April/012798.html

I have looked into the matter again and have tried everything I could  
think of. Now I am however able to describe the problem more in detail  
and more systematically. Tests have shown that the SECLR4 error occurs  
in all supercells containing bcc Fe and impurities, as long as the  
number of k points is high enough. Even if Fe itself is taken as an  
impurity, this is the case (the supercell is then pure iron). When the  
same size of supercell is taken, the problem always occurs at the same  
k point, independent of the value of RKMax or the chemical nature of  
the impurity. Most of the times this is the only k point where the  
error takes place (a parallel computation only fails for the  
subprocess containing that specific k point). Below an example is given.

For a pure Fe supercell containing 128 atoms (4x4x4 supercell, P  
sublattice), RKMax 7.0 and 10 k points in the IBZ (200 in the FBZ)  
runs without a glitch. When the converged case is restored in a new  
and empty directory and the number of k points is increased up to 56  
(2000 in the FBZ), the 2nd k point gives problems (and only that one):

          2         1         1         3        24 24.0

The first k point is computed correctly, giving:

      K=   0.04167   0.04167   0.04167            1
       MATRIX SIZE11270  WEIGHT= 8.00  PGR:
      EIGENVALUES ARE:
      -5.8279952   -5.8264711   -5.8264711   -5.8264462   -5.8262132
(...)
       1.9860526    1.9860593    1.9861886    1.9862001    1.9862001
       1.9862628    1.9897641    1.9897641    1.9897724    1.9897724
       1.9897768    1.9899170    1.9901205    1.9901205    1.9901247
             0 EIGENVALUES BELOW THE ENERGY  -10.00000
        ********************************************************

Afterwards the information of the 2nd k point is printed, resulting in:

  Matrix size        11235
          allocate HS       963.0 MB
          allocate Z        342.9 MB
      allocate spanel        11.0 MB          dimensions 11235   128
      allocate hpanel        11.0 MB          dimensions 11235   128
(...)
        allocate YL          65.8 MB          dimensions    15 11235    24
        allocate phsc         0.2 MB          dimensions 11235
Time for los      (hamilt) :         50.8
Time for alm         (hns) :          2.9
Time for vector      (hns) :         13.5
Time for vector2     (hns) :         11.9
Time for VxV         (hns) :        265.3
Wall Time for VxV    (hns) :          2.1
  Cholesky INFO =        10819

the last line being the SECLR4 error. Because this supercell only  
contains identical Fe atoms (at 14 artificially inequivalent  
positions) the number of possible changes in the case.in1 file is  
limited. Whatever I try, be it -in1ef or -in1_orig, with or without an  
additional d-LO, raising or lowering the linearization energies by 0,1  
Ry ..., nothing works and the SECLR4 error persists. With each test I  
started from a restore based on the case with 10 k points, using a new  
and empty directory.

I sincerely hope anyone can help me with this problem, that keeps  
hunting me in every supercell I need.

With kind regards

Kurt Lejaeghere
Ghent University, Belgium