Dear Laurence,
thank you for your detailed answer.
I have tried all your suggestions,
- I changed case.in0 with increased oversampling by factor two (new
parameters LUSE 26 and IFFTfactor 4)
------------ start of case.in0 -----------
TOT XC_LDA (XC_PBE,XC_PBESOL,XC_WC,XC_MBJ,XC_REVTPSSS)
NR2V IFFT 26 (R2V)
24 24 24 4.00 1 min IFFT-parameters, enhancement factor,
iprint
------------ end of case.in0 -----------
- I also tried to impose strong convergence criteria to be -cc
0.00000001 -ec 0.00000001
However, in both cases, the ghost MLD remains practically identical as
when using my default values (default Fe + convergence -cc 0.00001 -ec
0.000001)
Also, final :PUP 'Current' parameters remained practically the same for
all the calculations (by about 2 digits), being like (for M001)
PW CHANGE H K L Current Change Residue
:PUP001: 0 0 0 2.10719649E-02 5.090E-10 -7.530E-09
:PUP002: 0 -1 -1 3.67084665E-04 -7.004E-10 -3.572E-10
:PUP003: 1 -1 0 1.82124988E-04 -3.669E-10 -2.211E-10
:PUP004: 0 0 -2 -1.87471938E-03 6.192E-11 7.254E-10
:PUP005: 0 -2 0 -3.75090680E-03 1.125E-10 1.378E-09
:PUP006: 1 -1 -2 -3.46372731E-03 1.026E-10 1.378E-09
:PUP007: 1 -2 -1 -6.92804324E-03 2.418E-10 2.776E-09
:PUP008: 0 -2 -2 -7.14014083E-04 8.677E-11 2.032E-10
:PUP009: 2 -2 0 -3.57036516E-04 4.298E-11 1.121E-10
:PUP010: 0 -1 -3 2.62159615E-04 9.199E-11 -1.588E-10
:PUP011: 0 -3 -1 2.62289930E-04 9.844E-11 -1.555E-10
:PUP012: 1 -3 0 2.62219244E-04 9.133E-11 -1.551E-10
Unfortunately, all reflections seems to be allowed for bcc (H+K+L is
even), forbidden reflections of bcc are (H+K+L=odd), so I can not see
how they get close to zero ;-)) But the idea is excellent.
Thank you again and with my best regards
Jaroslav
On 27/11/17 15:27, Laurence Marks wrote:
Let me clarify slightly my comment about symmetry -- as I realized the
explanation (I think) and can also suggest something that might help.
First, concerning symmetry the explanation is I believe simple. If the
problem has a real symmetry operation such as inversion which is being
removed, then the Jacobian at the solution has zero's for charge
disturbances that break this symmetry. Because of this noise due to
numerical accuracy has a large effect, and almost certainly one has to
tighten the convergence criteria particularly -cc. You can monitor
this by looking at the :PUPXXX values in case.scfm and look how well
the forbidden reflections have converged to zero.
Second, do not be surprised about numerical issues. While the
calculations are done in double precision, there are many large sums
and in some cases double sums, and also numerical
integrations/differentiation. Any large sum or numerical
integration/differentiation in general reduces the numerical accuracy.
Hence even though double precision has an accuracy of 1D-15 the sum
may only be accurate to 1D-10 or even 1D-7. Also, the Intel ifort
compiler will reduce the numerical accuracy for speed if one is not
careful.
One thing that may help is to increase the oversampling in case.in0
for VXC, both that of the PW's and of the CLMs. A standard test is to
use LDA and see if the problem goes away, since oversampling is much
less relevant for this.
Of course your problem may have nothing to do with any of this....
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