Trouble with CELL_OPT with unit cells of different sizes

[Matt W]

Hi,

CP2K _currently_ doesn't have kpoints. This means that you need to use a 
relatively large unit cell to get sensible results. A bare minimum for Si 
is around 64 atoms I think, but that is certainly not large enough to 
converge the band gap or cohesive energies.

You need to keep expanding your supercell until the results are consistent.

Matt

On Saturday, February 7, 2015 at 9:50:22 PM UTC, Du Zhang wrote:
>
> Hi Zhendong,
>  
> Thanks for your suggestion! 
>  
> I tried without fixing the atom for Si2, and the geometry is 
>  
>
> i = 20, E = -7.6373030835
>
> Si 2.7020961928 0.9317906628 1.3251881238
>
> Si 0.0002037244 0.6283827813 -0.2219791667
>
> And the cell structure given by
>
> CELL| Volume [angstrom^3]: 111.629
>
> CELL| Vector a [angstrom]: 5.405 0.000 0.000 |a| = 5.405
>
> CELL| Vector b [angstrom]: 2.702 4.681 0.000 |b| = 5.405
>
> CELL| Vector c [angstrom]: 2.702 1.560 4.413 |c| = 5.405
>
> CELL| Angle (b,c), alpha [degree]: 60.000
>
> CELL| Angle (a,c), beta [degree]: 60.000
>
> CELL| Angle (a,b), gamma [degree]: 60.000
>
> CELL| Requested initial symmetry: RHOMBOHEDRAL
>
> CELL| Numerically orthorhombic: NO
>
> It seems that the bond length is still far too long.
>
> Any other thoughts on this from you all?
>
>  
>
> On Friday, February 6, 2015 at 11:14:44 AM UTC-4, Du Zhang wrote:
>
>> Hi Everyone,
>>  
>> I ran into some confusing results when I attempted to perform the 
>> following geometry optimizations on Si crystal with Si2 and Si8 unit cells. 
>>  
>> The input file for Si2:
>>  
>>
>> &GLOBAL
>>
>> PROJECT Si_bulk2
>>
>> RUN_TYPE CELL_OPT
>>
>> PRINT_LEVEL MEDIUM
>>
>> &END GLOBAL
>>
>> &FORCE_EVAL
>>
>> METHOD Quickstep
>>
>> STRESS_TENSOR ANALYTICAL
>>
>> &SUBSYS
>>
>> &KIND Si
>>
>> ELEMENT Si
>>
>> BASIS_SET DZVP-GTH-PADE
>>
>> POTENTIAL GTH-PADE-q4
>>
>> &END KIND
>>
>> &CELL
>>
>> A 3.83753393 0.00000000 0.00000000
>>
>> B 1.91876697 3.32340187 0.00000000
>>
>> C 1.91876697 1.10780062 3.13333333
>>
>> SYMMETRY RHOMBOHEDRAL
>>
>> PERIODIC XYZ
>>
>> &END CELL
>>
>> &COORD
>>
>> Si 1.91876697 1.10780062 0.78333333
>>
>> Si 0.00000000 -0.00000000 -0.00000000
>>
>> &END COORD
>>
>> &END SUBSYS
>>
>> &DFT
>>
>> BASIS_SET_FILE_NAME BASIS_SET
>>
>> POTENTIAL_FILE_NAME GTH_POTENTIALS
>>
>> &QS
>>
>> EPS_DEFAULT 1.0E-10
>>
>> &END QS
>>
>> &MGRID
>>
>> NGRIDS 4
>>
>> CUTOFF 300
>>
>> REL_CUTOFF 60
>>
>> &END MGRID
>>
>> &XC
>>
>> &XC_FUNCTIONAL PADE
>>
>> &END XC_FUNCTIONAL
>>
>> &END XC
>>
>> &SCF
>>
>> SCF_GUESS ATOMIC
>>
>> EPS_SCF 1.0E-7
>>
>> MAX_SCF 300
>>
>> ADDED_MOS 10
>>
>> &DIAGONALIZATION ON
>>
>> ALGORITHM STANDARD
>>
>> &END DIAGONALIZATION
>>
>> &MIXING T
>>
>> METHOD BROYDEN_MIXING
>>
>> ALPHA 0.4
>>
>> NBROYDEN 8
>>
>> &END MIXING
>>
>> &SMEAR ON
>>
>> METHOD FERMI_DIRAC
>>
>> ELECTRONIC_TEMPERATURE [K] 300
>>
>> &END SMEAR
>>
>> &END SCF
>>
>> &END DFT
>>
>> &PRINT
>>
>> &FORCES ON
>>
>> &END FORCES
>>
>> &END PRINT
>>
>> &END FORCE_EVAL
>>
>> &MOTION
>>
>> &CELL_OPT
>>
>> KEEP_ANGLES
>>
>> KEEP_SYMMETRY
>>
>> &END CELL_OPT
>>
>> &GEO_OPT
>>
>> TYPE MINIMIZATION
>>
>> MAX_DR 1.0E-03
>>
>> MAX_FORCE 1.0E-03
>>
>> RMS_DR 1.0E-03 
>>
>> RMS_FORCE 1.0E-03
>>
>> MAX_ITER 200
>>
>> OPTIMIZER BFGS
>>
>> !&BFGS
>>
>> ! MAX_STEEP_STEPS 0
>>
>> ! RESTART_LIMIT 9.0E-01
>>
>> !&END BFGS
>>
>> &END GEO_OPT
>>
>> &CONSTRAINT
>>
>> &FIXED_ATOMS
>>
>> COMPONENTS_TO_FIX XYZ
>>
>> LIST 2
>>
>> &END FIXED_ATOMS
>>
>> &END CONSTRAINT
>>
>> &END MOTION 
>>
>> Its initial cell structure is given by:
>>
>> CELL| Volume [angstrom^3]: 39.961
>>
>> CELL| Vector a [angstrom]: 3.838 0.000 0.000 |a| = 3.838
>>
>> CELL| Vector b [angstrom]: 1.919 3.323 0.000 |b| = 3.838
>>
>> CELL| Vector c [angstrom]: 1.919 1.108 3.133 |c| = 3.838
>>
>> CELL| Angle (b,c), alpha [degree]: 60.000
>>
>> CELL| Angle (a,c), beta [degree]: 60.000
>>
>> CELL| Angle (a,b), gamma [degree]: 60.000
>>
>> CELL| Requested initial symmetry: RHOMBOHEDRAL
>>
>> CELL| Numerically orthorhombic: NO
>>
>>  
>>
>> And its final cell structure is
>>
>> CELL| Volume [angstrom^3]: 137.274
>>
>> CELL| Vector a [angstrom]: 5.790 0.000 0.000 |a| = 5.790
>>
>> CELL| Vector b [angstrom]: 2.895 5.015 0.000 |b| = 5.790
>>
>> CELL| Vector c [angstrom]: 2.895 1.672 4.728 |c| = 5.790
>>
>> CELL| Angle (b,c), alpha [degree]: 60.000
>>
>> CELL| Angle (a,c), beta [degree]: 60.000
>>
>> CELL| Angle (a,b), gamma [degree]: 60.000
>>
>> CELL| Requested initial symmetry: RHOMBOHEDRAL
>>
>> CELL| Numerically orthorhombic: NO
>>
>>  
>>
>> And the final geometry is
>>
>> i = 45, E = -7.6936438860
>>
>> Si 4.1049115417 -0.4237817114 4.7278581917
>>
>> Si 0.0000000000 0.0000000000 0.0000000000
>>
>> The Si-Si length is clearly too long.
>>
>>  
>>
>>  
>>
>>  
>>
>>  
>>
>> For the Si8 case, things appear quite normal.
>>
>> Input:
>>
>> &GLOBAL
>>
>>  PROJECT Si_bulk8
>>
>>  RUN_TYPE CELL_OPT
>>
>>  PRINT_LEVEL MEDIUM
>>
>> &END GLOBAL
>>
>> &FORCE_EVAL
>>
>>  METHOD Quickstep
>>
>>  STRESS_TENSOR ANALYTICAL
>>
>>  &SUBSYS
>>
>>  &KIND Si
>>
>>  ELEMENT Si
>>
>>  BASIS_SET DZVP-GTH-PADE
>>
>>  POTENTIAL GTH-PADE-q4
>>
>>  &END KIND
>>
>>  &CELL
>>
>>  A 5.430697500 0.000000000 0.000000000
>>
>>  B 0.000000000 5.430697500 0.000000000
>>
>>  C 0.000000000 0.000000000 5.430697500
>>
>>  SYMMETRY CUBIC
>>
>>  PERIODIC XYZ
>>
>>  &END CELL
>>
>>  &COORD
>>
>>  Si 0.000000000 0.000000000 0.000000000
>>
>>  Si 0.000000000 2.715348700 2.715348700
>>
>>  Si 2.715348700 2.715348700 0.000000000
>>
>>  Si 2.715348700 0.000000000 2.715348700
>>
>>  Si 4.073023100 1.357674400 4.073023100
>>
>>  Si 1.357674400 1.357674400 1.357674400
>>
>>  Si 1.357674400 4.073023100 4.073023100
>>
>>  Si 4.073023100 4.073023100 1.357674400
>>
>>  &END COORD
>>
>>  &END SUBSYS
>>
>>  &DFT
>>
>>  BASIS_SET_FILE_NAME BASIS_SET
>>
>>  POTENTIAL_FILE_NAME GTH_POTENTIALS
>>
>>  &QS
>>
>>  EPS_DEFAULT 1.0E-10
>>
>>  &END QS
>>
>>  &MGRID
>>
>>  NGRIDS 4
>>
>>  CUTOFF 300
>>
>>  REL_CUTOFF 60
>>
>>  &END MGRID
>>
>>  &XC
>>
>>  &XC_FUNCTIONAL PADE
>>
>>  &END XC_FUNCTIONAL
>>
>>  &END XC
>>
>>  &SCF
>>
>>  SCF_GUESS ATOMIC
>>
>>  EPS_SCF 1.0E-7
>>
>>  MAX_SCF 300
>>
>>  ADDED_MOS 10
>>
>>  &DIAGONALIZATION ON
>>
>>  ALGORITHM STANDARD
>>
>>  &END DIAGONALIZATION
>>
>>  &MIXING T
>>
>>  METHOD BROYDEN_MIXING
>>
>>  ALPHA 0.4
>>
>>  NBROYDEN 8
>>
>>  &END MIXING
>>
>>  &SMEAR ON
>>
>>  METHOD FERMI_DIRAC
>>
>>  ELECTRONIC_TEMPERATURE [K] 300
>>
>>  &END SMEAR
>>
>>  &END SCF
>>
>>  &END DFT
>>
>>  &PRINT
>>
>>  &FORCES ON
>>
>>  &END FORCES
>>
>>  &END PRINT
>>
>> &END FORCE_EVAL
>>
>> &MOTION
>>
>>  &CELL_OPT
>>
>>  KEEP_ANGLES
>>
>>  KEEP_SYMMETRY
>>
>>  &END CELL_OPT
>>
>>  &GEO_OPT
>>
>>  TYPE MINIMIZATION
>>
>>  MAX_DR 1.0E-03
>>
>>  MAX_FORCE 1.0E-03
>>
>>  RMS_DR 1.0E-03 
>>
>>  RMS_FORCE 1.0E-03
>>
>>  MAX_ITER 200
>>
>>  OPTIMIZER BFGS
>>
>>  !&BFGS
>>
>>  ! MAX_STEEP_STEPS 0
>>
>>  ! RESTART_LIMIT 9.0E-01
>>
>>  !&END BFGS
>>
>>  &END GEO_OPT
>>
>>  &CONSTRAINT
>>
>>  &FIXED_ATOMS
>>
>>  COMPONENTS_TO_FIX XYZ
>>
>>  LIST 1
>>
>>  &END FIXED_ATOMS
>>
>>  &END CONSTRAINT
>>
>> &END MOTION 
>>
>>  Final cell structure:
>>
>> CELL| Volume [angstrom^3]: 173.162
>>
>> CELL| Vector a [angstrom]: 5.574 0.000 0.000 |a| = 5.574
>>
>> CELL| Vector b [angstrom]: 0.000 5.574 0.000 |b| = 5.574
>>
>> CELL| Vector c [angstrom]: 0.000 0.000 5.574 |c| = 5.574
>>
>> CELL| Angle (b,c), alpha [degree]: 90.000
>>
>> CELL| Angle (a,c), beta [degree]: 90.000
>>
>> CELL| Angle (a,b), gamma [degree]: 90.000
>>
>> CELL| Requested initial symmetry: CUBIC
>>
>> CELL| Numerically orthorhombic: YES
>>  
>> Final geometry
>>
>> i = 4, E = -31.3087094725
>>
>> Si 0.0000000000 0.0000000000 0.0000000000
>>
>> Si -0.0000000224 2.7868973667 2.7868973671
>>
>> Si 2.7868973677 2.7868973683 -0.0000000226
>>
>> Si 2.7868973673 -0.0000000224 2.7868973679
>>
>> Si 4.1803460577 1.3934486673 4.1803460580
>>
>> Si 1.3934486913 1.3934486907 1.3934486902
>>
>> Si 1.3934486666 4.1803460575 4.1803460574
>>
>> Si 4.1803460579 4.1803460580 1.3934486678
>>
>>  
>>
>> Could anyone help me with this confusion? Thanks a lot!
>>
>>  
>>
>>  
>>
>>  
>>
>>
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