[CP2K-user] [CP2K:14614] Re: Struggling to get SCF Convergence in Cell_Opt run
Travis
polla... at gmail.com
Fri Jan 22 08:41:12 UTC 2021
Hi,
For small band gap materials, you *need* to apply a broadening or smearing
function that smooths out the energy levels near the Fermi level so that
you don't oscillate between filling a low lying unoccupied level on one SCF
iteration, emptying it on the next, and so on and so on. There are multiple
methods for this such (refer to VASP manual for
example, https://www.vasp.at/wiki/index.php/ISMEAR), CP2K implements Fermi
smearing. You apply an electronic temperature that describes the shape of
the broadening function. *It isn't a physical temperature.*
-T
On Friday, January 22, 2021 at 3:19:27 AM UTC-5 ASSIDUO Network wrote:
> Then I cannot use smearing, I guess I'll have to turn it off or will have
> to talk to my supervisor about using a non-zero temperature.
>
> On Fri, Jan 22, 2021 at 10:17 AM Marcella Iannuzzi <ma... at gmail.com>
> wrote:
>
>>
>>
>> No smearing with 0K does not help.
>> Smearing needs a finite temperature, can be lower than 500, for instance
>> 300K, not 0K
>> On Friday, January 22, 2021 at 9:04:31 AM UTC+1 ASSIDUO Network wrote:
>>
>>> I'm going to follow your advice, but if I remember correctly, last time
>>> I tried smearing with 0 K, the stimulation ended with an error. If it does
>>> it again, I will ask for some feedback again.
>>>
>>> On Friday, January 22, 2021 at 9:59:40 AM UTC+2 Marcella Iannuzzi wrote:
>>>
>>>>
>>>>
>>>> Hi
>>>>
>>>> The smearing with finite electronic temperature is needed in order to
>>>> allow convergence of the metallic electronic structure, even if the
>>>> structure is kept a 0K. The number of added MOS depends on the density of
>>>> states around Fermi. Too many states do not hurt, in terms of convergence.
>>>> I just chose a safe number, probably less are also OK, as a lower smearing
>>>> temperature would also work.
>>>> As a functional I took one that I often use. Anyway, I think that
>>>> adding VDW is a good idea.
>>>> All these aspects are more general on electronic structure theory and
>>>> not specific of CP2K. Please read in the literature for better
>>>> understanding.
>>>> Regards
>>>> Marcella
>>>>
>>>>
>>>> On Friday, January 22, 2021 at 8:37:46 AM UTC+1 ASSIDUO Network wrote:
>>>>
>>>>> I should have added this earlier, the simulation must be performed at
>>>>> 0 K (my supervisor's request), it's a static run. Therefore, I cannot set
>>>>> the temperature to 500 K. Also, why the need for ADDED_MOS=200? In another
>>>>> thread, I was told that ADDED_MOS=100 was too much.
>>>>>
>>>>> Also, why the use of FUNCTIONAL XC_GGA_C_PBE and FUNCTIONAL
>>>>> XC_GGA_X_RPW86? I'm new to CP2K so just want to understand everything
>>>>> better.
>>>>> On Friday, January 22, 2021 at 9:24:10 AM UTC+2 Marcella Iannuzzi
>>>>> wrote:
>>>>>
>>>>>> Hi Lenard,
>>>>>>
>>>>>> I got it converging in 10 iterations.
>>>>>> The outer SCF with diagonalisation is useless, since there is no
>>>>>> preconditioner.
>>>>>> With metals you need to use smearing.
>>>>>> Here are some settings I used:
>>>>>> ADDED_MOS 200
>>>>>> &DIAGONALIZATION T
>>>>>> ALGORITHM STANDARD
>>>>>> &END DIAGONALIZATION
>>>>>> &MIXING T
>>>>>> METHOD BROYDEN_MIXING
>>>>>> ALPHA 0.01
>>>>>> BETA 0.5
>>>>>> NBUFFER 8
>>>>>> &END MIXING
>>>>>> &SMEAR
>>>>>> METHOD FERMI_DIRAC
>>>>>> ELECTRONIC_TEMPERATURE 500
>>>>>> &END SMEAR
>>>>>>
>>>>>> &XC
>>>>>> &XC_FUNCTIONAL
>>>>>> &LIBXC
>>>>>> FUNCTIONAL XC_GGA_X_RPW86
>>>>>> &END LIBXC
>>>>>> &LIBXC
>>>>>> FUNCTIONAL XC_GGA_C_PBE
>>>>>> &END LIBXC
>>>>>> &END XC_FUNCTIONAL
>>>>>>
>>>>>> &VDW_POTENTIAL
>>>>>> POTENTIAL_TYPE NON_LOCAL
>>>>>> &NON_LOCAL
>>>>>> CUTOFF 300
>>>>>> TYPE RVV10
>>>>>> ## VERBOSE_OUTPUT
>>>>>> KERNEL_FILE_NAME ${data}/rVV10_kernel_table.dat
>>>>>> &END NON_LOCAL
>>>>>> &END VDW_POTENTIAL
>>>>>> &END XC
>>>>>>
>>>>>> The results:
>>>>>>
>>>>>> Step Update method Time Convergence Total energy
>>>>>> Change
>>>>>>
>>>>>> ------------------------------------------------------------------------------
>>>>>> 1 NoMix/Diag. 0.10E-01 20.0 0.51067755
>>>>>> -133.2796876462 -1.33E+02
>>>>>> 2 Broy./Diag. 0.10E-01 17.6 0.00064724
>>>>>> -136.0334243526 -2.75E+00
>>>>>> 3 Broy./Diag. 0.10E-01 17.5 0.03257808
>>>>>> -134.7316158415 1.30E+00
>>>>>> 4 Broy./Diag. 0.10E-01 17.7 0.00019866
>>>>>> -133.0666478987 1.66E+00
>>>>>> 5 Broy./Diag. 0.10E-01 17.6 0.00228816
>>>>>> -133.1462861174 -7.96E-02
>>>>>> 6 Broy./Diag. 0.10E-01 17.6 0.00032933
>>>>>> -133.1654553845 -1.92E-02
>>>>>> 7 Broy./Diag. 0.10E-01 17.6 0.00000406
>>>>>> -133.1816175525 -1.62E-02
>>>>>> 8 Broy./Diag. 0.10E-01 17.7 0.00009047
>>>>>> -133.1825852315 -9.68E-04
>>>>>> 9 Broy./Diag. 0.10E-01 17.6 0.00000504
>>>>>> -133.1830490186 -4.64E-04
>>>>>> 10 Broy./Diag. 0.10E-01 17.6 0.00000031
>>>>>> -133.1828944498 1.55E-04
>>>>>>
>>>>>> *** SCF run converged in 10 steps ***
>>>>>>
>>>>>>
>>>>>> Electronic density on regular grids: -44.0000000000
>>>>>> 0.0000000000
>>>>>> Core density on regular grids: 43.9999999999
>>>>>> -0.0000000001
>>>>>> Total charge density on r-space grids: -0.0000000001
>>>>>> Total charge density g-space grids: -0.0000000001
>>>>>>
>>>>>> Overlap energy of the core charge distribution:
>>>>>> 0.00000001219968
>>>>>> Self energy of the core charge distribution:
>>>>>> -231.41335460772382
>>>>>> Core Hamiltonian energy:
>>>>>> 74.19344628639691
>>>>>> Hartree energy:
>>>>>> 45.27318657026385
>>>>>> Exchange-correlation energy:
>>>>>> -21.30000506759340
>>>>>> Dispersion energy:
>>>>>> 0.06400174824714
>>>>>> Electronic entropic energy:
>>>>>> -0.00016939092888
>>>>>> Fermi energy:
>>>>>> 0.34714684334798
>>>>>>
>>>>>> Total energy:
>>>>>> -133.18289444982969
>>>>>>
>>>>>>
>>>>>>
>>>>>> Regards
>>>>>> Marcella
>>>>>>
>>>>>> On Friday, January 22, 2021 at 6:48:12 AM UTC+1 ASSIDUO Network wrote:
>>>>>>
>>>>>>> Hi there everyone, hope you've had a great week.
>>>>>>>
>>>>>>> I've been trying to run a cell optimization of bulk Au, and I am
>>>>>>> using the attached input file, but I'm not getting an inner loop SCF
>>>>>>> convergence. I've made many small changes, such as including/excluding
>>>>>>> OUTER_SCF, changing the SCF convergence criterion, changing the number of
>>>>>>> cell optimization steps, changing the number of KPoints and changing the
>>>>>>> mixing method. Nothing has worked. I haven't tried a combination of the
>>>>>>> above though.
>>>>>>>
>>>>>>> Do you perhaps have any suggestions to me on how to get convergence?
>>>>>>> Furthermore, I would also appreciate some tips to speed up my simulations
>>>>>>> (settings/flags) wise.
>>>>>>>
>>>>>>> Thanks in advance,
>>>>>>> Lenard
>>>>>>>
>>>>>>>
>>>>>>> --
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>
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