[Wien] lapw1 runs too slow for H2 molecule

[Laurence Marks]

The reason is your value for RKMAX.

To expand, the largest k-value in lapw1 is determined by
RKMAX/min(RMT) which for H2 is 7/0.71. Probably when you did H you had
a larger RMT (probably 2.0), so the largest k was 7/2.0 which is about
3 times smaller. Since the size of the matrix you are diagonalizing
scales roughly as k**3, for H2 you have a matrix about 27 times larger
so it will probably take at least 50 time longer.

You can approximately use an RKMAX such that RKMAX/min(RMT) is about
the same, i.e. for your H2 molecule use an RKMAX of 2 or 2.5.
Unfortunately it is not quite as simple as this and larger RKMAX is
better.

Note as well that if you want to calculate the atomization energy of
H2 you MUST use the same RMT and RKMAX for both H and H2, otherwise
your energies are GIGO.

N.B., running systems with small RMTs with Wien2k, e.g. for H, is not easy.

On Fri, Oct 10, 2008 at 8:23 AM, Yurko Natanzon
<yurko.natanzon at gmail.com> wrote:
> Dear wien2k users,
> I'm running a simple exercise with H2 molecule located in the middle
> of a cubic box with a=15 Bohr. the H-H bond length is set to about
> 0.75 Ang and RMT radus is 0.71 (also the smaller values were tested).
>
> The problem is that the calculation is too long. It takes 40 minutes
> for LAPW1 to run:
> :log
>>   (runsp_lapw) options:
> Fri Oct 10 11:41:58 CEST 2008> (x) lapw0
> Fri Oct 10 11:42:21 CEST 2008> (x) lapw1 -c -up
> Fri Oct 10 12:20:05 CEST 2008> (x) lapw1 -c -dn
> Fri Oct 10 12:58:24 CEST 2008> (x) lapw2 -c -up
> Fri Oct 10 12:58:28 CEST 2008> (x) lapw2 -c -dn
> Fri Oct 10 12:58:31 CEST 2008> (x) lcore -up
> Fri Oct 10 12:58:31 CEST 2008> (x) lcore -dn
> Fri Oct 10 12:58:31 CEST 2008> (x) mixer
> For comparison, the same calculation for one H atom in the box  takes
> 3 seconds (lapw1), for CoO (a=8 Bohr) - just 12 seconds.
>
> I used init_lapw -numk 1 -vxc 13
> I post my in0 and in1 files as well as a struct file:
> --------------in0
> TOT   13    (5...CA-LDA, 13...PBE-GGA, 11...WC-GGA)
> NR2V      IFFT      (R2V)
>  -1 -1 -1    1.00    min IFFT-parameters, enhancement factor  #changed
> the default values because of IFFT errors
> ---------------in1c
> WFFIL        (WFPRI, SUPWF)
>  7.00       10    4 (R-MT*K-MAX; MAX L IN WF, V-NMT
>  0.30    1  0      (GLOBAL E-PARAMETER WITH n OTHER CHOICES, global APW/LAPW)
>  0    0.30      0.000 CONT 1
>  0.30    1  0      (GLOBAL E-PARAMETER WITH n OTHER CHOICES, global APW/LAPW)
>  0    0.30      0.000 CONT 1
> K-VECTORS FROM UNIT:4   -9.0       2.0     7   emin/emax/nband
> --------------------struct file
> h2 molecule
> P   LATTICE,NONEQUIV.ATOMS:  2
> MODE OF CALC=RELA unit=bohr
>  15.117815 15.117815 15.117815 90.000000 90.000000 90.000000
> ATOM  -1: X=0.45300000 Y=0.50000000 Z=0.50000000
>          MULT= 1          ISPLIT=-2
> H 1        NPT=  781  R0=0.00010000 RMT=    0.7100   Z:  1.0
> LOCAL ROT MATRIX:    0.0000000 0.0000000 1.0000000
>                     0.0000000 1.0000000 0.0000000
>                    -1.0000000 0.0000000 0.0000000
> ATOM  -2: X=0.54700000 Y=0.50000000 Z=0.50000000
>          MULT= 1          ISPLIT=-2
> H 1        NPT=  781  R0=0.00010000 RMT=    0.7100   Z:  1.0
> LOCAL ROT MATRIX:    0.0000000 0.0000000 1.0000000
>                     0.0000000 1.0000000 0.0000000
>                    -1.0000000 0.0000000 0.0000000
>   8      NUMBER OF SYMMETRY OPERATIONS
>  1 0 0 0.00000000
>  0-1 0 0.00000000
>  0 0-1 0.00000000
>       1
>  1 0 0 0.00000000
>  0-1 0 0.00000000
>  0 0 1 0.00000000
>       2
>  1 0 0 0.00000000
>  0 0-1 0.00000000
>  0-1 0 0.00000000
>       3
>  1 0 0 0.00000000
>  0 0 1 0.00000000
>  0-1 0 0.00000000
>       4
>  1 0 0 0.00000000
>  0 0-1 0.00000000
>  0 1 0 0.00000000
>       5
>  1 0 0 0.00000000
>  0 0 1 0.00000000
>  0 1 0 0.00000000
>       6
>  1 0 0 0.00000000
>  0 1 0 0.00000000
>  0 0-1 0.00000000
>       7
>  1 0 0 0.00000000
>  0 1 0 0.00000000
>  0 0 1 0.00000000
>       8
> --------------------
>
> With best regards,
> Yurko
>
> --
> Yurko (aka Yuriy, Iurii, Jurij etc) Natanzon
> PhD Student
> Henryk Niewodniczan`ski Institute of Nuclear Physics
> Polish Academy of Sciences
> ul. Radzikowskiego 152,
> 31-342 Krako`w, Poland
> Email: Yurii.Natanzon at ifj.edu.pl, yurko.natanzon at gmail.com
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>



-- 
Laurence Marks
Department of Materials Science and Engineering
MSE Rm 2036 Cook Hall
2220 N Campus Drive
Northwestern University
Evanston, IL 60208, USA
Tel: (847) 491-3996 Fax: (847) 491-7820
email: L-marks at northwestern dot edu
Web: www.numis.northwestern.edu
Chair, Commission on Electron Crystallography of IUCR
www.numis.northwestern.edu/
Electron crystallography is the branch of science that uses electron
scattering to study the structure of matter.