[CP2K-user] EXTERNAL_PRESSURE and PRESSURE_TOLERANCE settings in cell optimisations for crystals

[Huaiyang Sun]

Dear Fabian,
Thanks for the explanation! I've noticed the CELL_REF and OT issues of the 
input file. The CP2K output file also hints about the OT algorithm.   
The reason I use DZV-GTH-PADE basis for Y is that I cannot find GTH-PBE 
basis set for it in the cp2k/data directory. Maybe I should find the 
corresponding basis set in somewhere else.
Anyway, thanks for your help and suggestions!

Best regards.
Huaiyang Sun

On Wednesday, November 25, 2020 at 3:26:58 PM UTC+8 fa... at gmail.com 
wrote:

> Dear Huaiyang Sun,
>
> Many solids have a bulk modulus in the range of 1 to 100 GPa. A material 
> with a bulk modulus of 10 GPa changes its volume by 1% when subjected to a 
> pressure of 1000 bar. In this case a PRESSURE_TOLERANCE of 100 bar is 
> already accurate to within 0.1% of the volume.
>
> The input file has some issues:
> use CELL_REF for a cell optimization
> you cannot use OT together with k-points, use DIAGONALIZATION instead
> I would recomment to not mix different basis sets, especially not using 
> PADE ones for PBE calculations
>
> Cheers,
> Fabian
> On Wednesday, 25 November 2020 at 04:09:02 UTC+1 sh... at gmail.com wrote:
>
>>
>> Deal all,
>>
>> I'm doing a cell optimisation run of a YAG (Y3Al5O12) crystal. I wonder 
>> about the meaning of the tags EXTERNAL_PRESSURE and PRESSURE_TOLERANCE in 
>> the CELL_OPT section of the input. The default values are both 100 bar. 
>> Here are the few points I don't understand,
>>
>> 1. If the cell optimisation run is targeted at the input 
>> EXTERNAL_PRESSURE, shouldn't the default PRESSURE_TOLERANCE be given a much 
>> smaller value, like 5.0 or 1.0 bar?
>>
>> 2. Why 100 bar? 1 atm = 1.013 bar sounds more reasonable.
>>
>> 3. My simple understanding of cell optimisation is to find the minimum 
>> point of the energy-volume (E-V) curve. Then what's the role of external 
>> pressure?
>>
>> Here is my input file.
>>
>> &GLOBAL
>>   project  pristine-opt
>>   run_type CELL_OPT
>>   print_level MEDIUM
>> &END GLOBAL
>>
>> &FORCE_EVAL
>>   METHOD QS
>>
>>   &SUBSYS
>>     &CELL 
>>       ABC  12.0003 12.0003 12.0003  
>>       PERIODIC XYZ 
>>       MULTIPLE_UNIT_CELL  1   1   1
>>       SYMMETRY CUBIC 
>>     &END CELL
>>
>>     &TOPOLOGY
>>       MULTIPLE_UNIT_CELL  1   1   1
>>       COORD_FILE_FORMAT XYZ
>>       COORD_FILE_NAME yag_from_cif_conven_unit.xyz 
>>     &END TOPOLOGY
>>
>>     &KIND Y
>>       ELEMENT Y
>>       BASIS_SET DZV-GTH-PADE
>>       POTENTIAL GTH-PBE-q11
>>     &END KIND 
>>
>>
>>     &KIND Al
>>       ELEMENT Al
>>       BASIS_SET DZVP-MOLOPT-SR-GTH 
>>       POTENTIAL GTH-PBE-q3
>>     &END KIND 
>>
>>     &KIND O
>>       ELEMENT O
>>       BASIS_SET DZVP-GTH-PBE
>>       POTENTIAL GTH-PBE-q6
>>     &END KIND
>>
>>     &KIND Ce
>>       ELEMENT Ce
>>       BASIS_SET DZVP-MOLOPT-SR-GTH-q12
>>       POTENTIAL GTH-PBE-q12
>>     &END KIND
>>
>>     &KIND Yb
>>       ELEMENT Yb
>>       BASIS_SET DZVP-MOLOPT-SR-GTH-q24
>>       POTENTIAL GTH-PBE-q24
>>     &END KIND
>>
>>   &END SUBSYS
>>
>>   &DFT
>>     BASIS_SET_FILE_NAME BASIS_SET_YAG
>>     POTENTIAL_FILE_NAME POTENTIAL_YAG
>>
>>     &MGRID
>>       NGRIDS 4
>>       CUTOFF 600
>>       REL_CUTOFF 60
>>     &END MGRID
>>
>>     &QS
>>       EPS_DEFAULT 1.0E-12
>>     &END QS
>>
>>     &POISSON
>>       PERIODIC XYZ
>>     &END POISSON
>>
>>     &SCF
>>       SCF_GUESS ATOMIC
>>       EPS_SCF 5.0E-7
>>       MAX_SCF 200 
>>
>>       CHOLESKY INVERSE 
>>
>>       &OT ON
>>         MINIMIZER DIIS
>>       &END OT
>>       #&DIAGONALIZATION 
>>       #  ALGORITHM STANDARD
>>       #&END DIAGONALIZATION 
>>
>>       # ADDED_MOS 30
>>       #
>>       # &SMEAR ON
>>       # METHOD FERMI_DIRAC
>>       # ELECTRONIC_TEMPERATURE [K] 300
>>       #&END SMEAR 
>>
>>       # &MIXING
>>       #  METHOD BROYDEN_MIXING
>>       #  ALPHA 0.4
>>       #  BETA 0.5
>>       #  NBROYDEN 8
>>       # &END MIXING 
>>     &END SCF
>>
>>     &XC
>>       &XC_FUNCTIONAL PBE
>>       &END XC_FUNCTIONAL 
>>     &END XC
>>
>>     &KPOINTS
>>       EPS_GEO 1.0E-5
>>       SCHEME MONKHORST 3 3 3
>>     &END KPOINTS
>>   &END DFT
>>
>>   &PRINT
>>     &TOTAL_NUMBERS ON
>>     &END TOTAL_NUMBERS
>>   &END PRINT
>>   
>>   STRESS_TENSOR ANALYTICAL 
>> &END FORCE_EVAL
>>
>> &MOTION
>>   &GEO_OPT
>>     OPTIMIZER LBFGS
>>     TYPE MINIMIZATION
>>     MAX_DR   5.0E-4
>>     MAX_FORCE 5.0E-4
>>     RMS_DR  5.0E-4
>>     RMS_FORCE 5.0E-4
>>     MAX_ITER 500
>>   &END GEO_OPT
>>
>>   &CELL_OPT
>>     TYPE DIRECT_CELL_OPT
>>     OPTIMIZER LBFGS
>>     KEEP_SYMMETRY
>>     MAX_DR 5.0E-4
>>     MAX_FORCE 1.0E-4
>>     RMS_DR 5.0E-4
>>     RMS_FORCE 5.0E-4
>>     # defaults for p and delta p [bar]
>>     EXTERNAL_PRESSURE   100.0 0.0 0.0    0.0 100.0 0.0   0.0 0.0 100.0
>>     PRESSURE_TOLERANCE  100.0
>>   &END CELL_OPT
>> &END MOTION 
>>
>>
>>
>>
>> Thank you,
>> Huaiyang Sun
>>
>>
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