[CP2K:5395] Re: graphite in CP2K

[Michele Ceriotti]

Dear Matt (and Marcella who basically replied the same in private),

   Thanks a million, using the molopt basis set does fix things. I had
tried both the dzvp from basis_sets and gth_basis_set, and I was getting
similar nonsense.

I am a bit scared seeing how much difference it makes changing the basis
set. Any idea why graphite should be such a nasty beast? I had experimented
with different basis sets for water and never saw such a dramatic effect.

All the best,
Michele
On 28 May 2014 19:23, "Matt W" <MattWa... at gmail.com> wrote:

> Hi Michele,
>
> please try using the MOLOPT basis sets provided with CP2K
> ($CP2K_root/tests/QS/BASIS_MOLOPT) that prehaps give a more suitable
> starting point for describing a "molecular" system like graphite than
> atomic optimization based ones.
>
> Using a DZVP-MOLOPT-SR-GTH basis - I get SCF convergence in ~10 cycles and
> geometry converges in ~10 steps (with BFGS).
>
> Matt
>
> On Wednesday, May 28, 2014 5:19:30 PM UTC+1, Michele Ceriotti wrote:
>>
>> 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" <matth... 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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