[CP2K-user] Struggling to get SCF Convergence in Cell_Opt run

[Marcella Iannuzzi]

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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