Cell Optimization of triclinic cell

[Matt W]

Hi,

you should either specify 

ABC and alpha, beta, gamma

or

give the whole set of vectors, not both.

If the set of A, B, C vectors are given any angles are ignored.

Also, I suspect  your supercell likely isn't large enough. By default cp2k 
only uses gamma point to sample the Brillouin zone. You should probably use 
a 2x2x1 supercell to get reasonably accurate results.

Matt

On Wednesday, April 18, 2018 at 12:03:43 AM UTC+1, Aniruddha Dive wrote:
>
> Hi All,
>
> I am trying to do cell optimization of a SiS2 crystal structure which has 
> a triclinic symmetry. Below is the section of input file where I specify 
> the cell vectors and the angles:
>
>  &SUBSYS
>     &CELL
>       
>
>
>
>
> *SYMMETRY TRICLINIC      A 5.58515   0.00000   0.00000      B 0.00000   
> 6.21427   0.00000      C 0.00000   0.00000  10.92676      ALPHA_BETA_GAMMA 
> 116.86 113.96 90.00      PERIODIC XYZ*
>     &END
>     ! unit cells that are orthorhombic are more efficient with CP2K
>     ! atom coordinates can be in the &COORD section,
>     ! or provided as an external file.
>     &TOPOLOGY
>        COORD_FILE_FORMAT PDB
>        COORD_FILE_NAME SiS2_computed.pdb
>        CONNECTIVITY OFF
>        &CENTER_COORDINATES
>        &END CENTER_COORDINATES
>     &END
>
> When I try to run the calculations, in the output file I can see the 
> correct vectors a,b and c but the angles are still 90.0 90.0 and 90.0. 
> Below is the portion from output file:
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> *CELL_TOP| Volume [angstrom^3]:                                          
> 379.242 CELL_TOP| Vector a [angstrom     5.585     0.000     0.000    |a| 
> =       5.585 CELL_TOP| Vector b [angstrom     0.000     6.214     0.000    
> |b| =       6.214 CELL_TOP| Vector c [angstrom     0.000     0.000    
> 10.927    |c| =      10.927 CELL_TOP| Angle (b,c), alpha 
> [degree]:                                   90.000 CELL_TOP| Angle (a,c), 
> beta  [degree]:                                   90.000 CELL_TOP| Angle 
> (a,b), gamma [degree]:                                   90.000 CELL_TOP| 
> Requested initial symmetry:                                 
> TRICLINIC CELL_TOP| Numerically 
> orthorhombic:                                         YES CELL| Volume 
> [angstrom^3]:                                              379.242 CELL| 
> Vector a [angstrom]:       5.585     0.000     0.000    |a| =       
> 5.585 CELL| Vector b [angstrom]:       0.000     6.214     0.000    |b| 
> =       6.214 CELL| Vector c [angstrom]:       0.000     0.000    10.927    
> |c| =      10.927 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:                                     
> TRICLINIC CELL| Numerically 
> orthorhombic:                                             YES CELL_REF| 
> Volume [angstrom^3]:                                          
> 379.242 CELL_REF| Vector a [angstrom     5.585     0.000     0.000    |a| 
> =       5.585 CELL_REF| Vector b [angstrom     0.000     6.214     0.000    
> |b| =       6.214 CELL_REF| Vector c [angstrom     0.000     0.000    
> 10.927    |c| =      10.927 CELL_REF| Angle (b,c), alpha 
> [degree]:                                   90.000 CELL_REF| Angle (a,c), 
> beta  [degree]:                                   90.000 CELL_REF| Angle 
> (a,b), gamma [degree]:                                   90.000 CELL_REF| 
> Requested initial symmetry:                                 
> TRICLINIC CELL_REF| Numerically 
> orthorhombic:                                         YES*
>
> Because of this the complete geometry of the cell has changed during the 
> optimization giving me weird results. Please find attached input files as 
> well as the coordinate file.
>
> Kindly let me know how to fix the issue.
>
> Regards,
> Aniruddha M Dive
> PhD Candidate, Washington State University
>
>
>
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