[CP2K:5393] Re: graphite in CP2K

[Michele Ceriotti]

Hi Matthias,
   Thanks for the quick answer. I have already played with the obvious
parameters, point is it is impossible to converge the scf properly.
Everything looks like what you get when the geometry is crazy, and indeed
my student tried to enlarge the cell (by almost 10%!) and got  converged
scf and more reasonable forces.
However this is inconsistent with the literature and the results from
siesta.
We have been trying to fiddle with the scf parameters for days, but get
consistently 100au forces on a geometry that should be very close to
optimum.
Do you see something wrong with how we define the cell or the positions?
Best
Michele
On 28 May 2014 17:47, "Matthias Krack" <matthia... at psi.ch> wrote:

> Hi Michele,
>
> I would suggest to set EPS_DEFAULT in @QS section at least to 1.0E-12 or
> lower and for the ALPHA in &MIXING I would also use a smaller value like
> 0.2. Maybe this will help to converge your system properly.
>
> Matthias
>
> On Wednesday, May 28, 2014 4:20:44 PM UTC+2, Michele Ceriotti wrote:
>>
>> Dear CP2K community,
>>
>>      I have been trying for a few days to set up calculations of graphite
>> as an exercise for a student but I am getting the weirdest results.  I am
>> sure in the it will end up being a silly mistake in the input, but I can't
>> get to see it so perhaps someone can help.
>>
>> Despite using a fairly large FD smearing, the SCF cycle has a hard time
>> converging, and when the maximum number of steps is reached
>>
>>     50 Broy./Diag. 0.50E+00    1.2     0.00014351      -819.2909959720
>> -2.28E-09
>>   *** SCF run NOT converged ***
>>
>> and the calculation carries on with what it has got, diagnostics are
>> really strange.
>>
>> For a start, eigenvalues show two weird very low-energy states
>>  MO EIGENVALUES AND MO OCCUPATION NUMBERS
>> # MO index          MO eigenvalue [a.u.]            MO occupation
>>          1                    -21.523076                 2.000000
>>          2                    -21.517160                 2.000000
>>          3                     -1.383548                 2.000000
>>          4                     -0.510418                 2.000000
>>
>> forces on the atoms are insane
>>  ATOMIC FORCES in [a.u.]
>>  # Atom   Kind   Element          X              Y              Z
>>       1      1      C           4.68736611     4.63921800  -222.86999309
>>       2      1      C          -1.57720920    -4.48651652   124.33822840
>>       3      1      C          -5.01734639     3.10518104   176.16292919
>>
>> and so is the stress tensor
>>  STRESS TENSOR [GPa]
>>             X               Y               Z
>>   X   -8233.84728056      8.05482610      0.90481573
>>   Y       8.05482610  -9552.76932222     -0.49445437
>>   Z       0.90481573     -0.49445437  -2526.59040628
>>
>> I was thinking of an error in the structure or the cell parameters, but I
>> checked it many times and everything seems in order. The same structure,
>> with same functional and similar parameters in SIESTA converges like a
>> stone, and gives no problem whatsoever.
>>
>> Can you spot something obvious that I am missing? I'd really like to use
>> CP2K for this exercise, but I can't seem to figure out what is going wrong.
>>
>> Many thanks,
>> Michele
>>
>>  --
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