[Pw_forum] Regarding supercell dimensions

[mohnish pandey]

Dear Deepak!

There no cell parameter in your input. You have to take the experimental
value of the lattice constant available or dig out some paper in which the
relevant calculations are done. See the INPUT_PW.txt in DOC folder of
espresso distribution. The meaning of parameters are very clearly mentioned
there. And next time please mention your affiliation so that we should know
whom we are interacting with.

On Wed, Aug 3, 2011 at 11:19 PM, dipak thakur <deepak.p.thakur at gmail.com>wrote:

> I am nobe to quantum espresso and using supercell for first time.
> Can any one help me in understanding few things regarding the supecell
> determination?
>
> The following is a typical input file I am using (copied from one of the
> earlier post).
>
> CONTROL
>   title = 'Graphene mono layer'
>   calculation =   "relax"   ,
>   restart_mode = 'from_scratch' ,
>   outdir='/home/usuarios/baldini/espresso-4.2.1/tmp/' ,
>   pseudo_dir = '/home/usuarios/baldini/espresso-4.2.1/pseudo' ,
>
>               etot_conv_thr = 1.0E-4  ,
>               forc_conv_thr = 1.0D-3 ,
>               nstep=50,
>               dt=40,
>               prefix='1MLG_Ti_H2',
> /
> &SYSTEM
>                       ibrav = 0.,
>
>                       ntyp = 2 ,
>                       nat = 33 ,
>                       ecutwfc = 50.0 ,
>                       ecutrho = 400.0,
> /
> &ELECTRONS
>             electron_maxstep = 300.,
>             conv_thr  =  1.0d-8  ,
>
>             mixing_mode = 'plain',
>             mixing_beta = 0.5,
>             diagonalization   =   'cg' ,
>             diago_cg_maxiter = 50,
> /
> &IONS
> /
> CELL_PARAMETERS
> 16.12131954   9.383047808   0.0000000
>
> 0.00000000  18.658162370   0.0000000
> 0.0000000    0.0000000    56.6893424
> ATOMIC_SPECIES
> C   12.0107   C.pbe-van_ak.UPF
> Ti  47.8670   Ti.pbe-sp-van_ak.UPF
> ATOMIC_POSITIONS angstrom
> C      2.89163        7.40219        1.8862
>
> C      3.59292        8.63832        1.8826
> C      3.60349        6.16702        1.8884
> C      5.0186         8.64501        1.8612
> C      5.0215         6.16598        1.8904
> C      5.73302        7.40522        1.8718
>
> C      1.47184        7.39616        1.891
> C      2.89112        9.87066        1.886
> C      2.89471        4.93264        1.8916
> C      5.73319        9.8885         1.8612
> C      5.73643        4.9413         1.8924
>
> C      7.16348        7.41203        1.882
> C      1.47474        4.9269         1.8924
> C      0.762281       8.62783        1.8946
> C      0.763134       6.16172        1.8914
> C      1.4715         9.86335        1.8934
>
> C      3.60341        11.1095        1.8868
> C      5.02124        11.1239        1.882
> C      3.60512        3.70156        1.8932
> C      5.02645        3.70789        1.891
> C      7.87807        8.65532        1.8816
>
> C      7.16373        9.89497        1.872
> C      7.16203        4.94814        1.8954
> C      7.87619        6.17677        1.8996
> C      5.73634        12.3522        1.8872
> C      0.772689       3.69102        1.898
>
> C      0.762793       1.22003        1.8968
> C      7.87645        11.1337        1.8894
> C      7.16203        12.3587        1.889
> C      7.87201        13.5922        1.8942
> C      2.89479        2.46619        1.8922
>
> C      1.47482        2.45878        1.8952
> Ti     6.41604        8.65974        3.74
> K_POINTS {automatic}
> 6.0 6.0 1.0 1.0 1.0 1.0
>
> Can anyone help me understanding how are these Cell parameters calculated?
>
> Also in some cases celld(m) are used. Can anyone comment on these also?
> How are the cell parameters and lattice constant or atomic spacing related?
>
> Any clue would be of great help.
>
> Thanks in advance.
>
>
> Rgds
> Deepak
>
>
>
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>


-- 
Regards,
MOHNISH,
-----------------------------------------------------------------
Mohnish Pandey
Senior Project Associate,
Department of Chemical Engineering,
IIT KANPUR, UP, INDIA
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