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

[fa...@gmail.com]

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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