total charge incorrect

[Ronald Cohen]

Hello! I am finding that Elk (6.8.4) prints finds the incorrect total charge. At first I thought it was an input problem, or a compiler problem, but I have now tested with a number of systems including examples that come with elk and with different compilers and on different computers and find the same thing. I was not able to find this in the forum, but maybe I missed it? So for example, with the BaTiO3 example using the species files that come with elk, I find in INFO.OUT:EIGVAL.OUT:
  25  0.3179749728      2.000000000   
    26  0.4086095182      0.5155550937E-16
etc for each k-point. So it should come out with an even number of electrons. If it were a metal the Fermi level should be adjusted to give the correct charge, but we find for Iridium:

and Pt:

total calculated charge    :    77.99263752 

total calculated charge    :    102.0243043 

whereas the charge should be 102.

Sometimes the charge is real terrible. For example in the BaTiO3 example, if I increase gmaxvr from 18 to 22 it gets much worse:

total calculated charge    :    51.99999409   
total calculated charge    :    51.99999449   
total calculated charge    :    51.99999964   
total calculated charge    :    51.99999982   
total calculated charge    :    81.66752526   
total calculated charge    :    101.9951334   

So this means that the fft is messing up? However I tried switching fft libraries and get the same result.

I do not understand how it can be fractional as it is an insulator and the states are all occupied correctly:

total calculated charge    :    76.98870966   
total calculated charge    :    65.19357430   
total calculated charge    :    47.99985111   
total calculated charge    :    78.01516460   
total calculated charge    :    77.93958531   
total calculated charge    :    72.03920900   
total calculated charge    :    74.24595460

Can someone please explain what is happening and how to fix it? Surprisingly the total energies seem OK, so it is just the printed value wrong?

By the way, I have over 30 years experience with LAPW, mainly with the Krakauer, Singh, and WIEN2K codes, and I never saw this before.

Ronald Cohen
Earth and Planets Laboratory
Carnegie Institution for Science

[Ronald Cohen]

I also find this problem with elk version 6.3.2, but with the same input the errors are different:

cohen@tomcat:/home/beegfs/rcohen/ELK/PTO/WCP0/WClibXC/static$ grep "total calculated" INFO.OUT.6.8.3 | head
total calculated charge : 128.0155108
total calculated charge : 128.0155731
total calculated charge : 128.0155682
total calculated charge : 128.0156023
total calculated charge : 128.0155967
total calculated charge : 128.0144846
total calculated charge : 128.0171201
total calculated charge : 127.9950034
total calculated charge : 128.0115674
total calculated charge : 128.0153518
rcohen@tomcat:/home/beegfs/rcohen/ELK/PTO/WCP0/WClibXC/static$ grep "total calculated" INFO.OUT.6.3.2 | head
total calculated charge : 127.9992115
total calculated charge : 128.1297140
total calculated charge : 128.4487872
total calculated charge : 128.9908332
total calculated charge : 129.0412120
total calculated charge : 129.1197192
total calculated charge : 129.0372176
total calculated charge : 128.0112899
total calculated charge : 128.0550725

--Ron Cohen

[Ronald Cohen]

Increasing lmax lmaxapw to 12 from 8 also doesn't help.

[Ronald Cohen]

This is wild—it gets worse with higher rkmax (rgkmax) ! I think the problem is overcompletness of the basis set. The Cholesky gets illdetermined if rkmax is too high
and this depends also onthe number of local orbitals.

For PbTiO3 with rkmax=7 the charge is better and it converges in 24 iterations.
total calculated charge : 128.0138943

with rkmax=9
The charge is wrong and it doesn’t converge in 200 iterations!
total calculated charge : 124.7882743

even rkmax=8 seems too high
total calculated charge : 128.0154127
total calculated charge : 128.0154729
total calculated charge : 128.0154702
total calculated charge : 128.0132205
total calculated charge : 128.0669213
total calculated charge : 128.1216375
total calculated charge : 128.0025878
total calculated charge : 128.0113803
total calculated charge : 128.0093243
total calculated charge : 128.0245623
total calculated charge : 128.0348816
total calculated charge : 128.0017551
total calculated charge : 128.0108920
total calculated charge : 128.0084946
total calculated charge : 128.0961536
total calculated charge : 113.4393557

This is related probably due to the interaction with the local orbitals in the default species file.

Ron

[J. K. Dewhurst]

Hi Ron,

I ran BaTiO3 with:

tasks
  0

highq
 .true.

ngridk
  8  8  8

avec
  7.576  0.0    0.0
  0.0    7.576  0.0
  0.0    0.0    7.576

atoms
  3                                    : nspecies
  'Ba.in'                              : spfname
  1                                    : natoms; atpos below
  0.0  0.0  0.0
  'Ti.in'
  1
  0.5  0.5  0.5
  'O.in'
  3
  0.5  0.5  0.0
  0.5  0.0  0.5
  0.0  0.5  0.5

... and everything seems fine. The calculated total charge from the last iteration was 102.0017678, which is well within tolerance.

Could you post your problematic input files and I'll run them?

Regards,
Kay.