[Pw_forum] Help regarding supercell

Duy Le ttduyle at gmail.com
Thu Aug 4 19:13:23 CEST 2011


If ibrav=0, you must NOT specify celldm(2-6), according to the manual.
http://www.quantum-espresso.org/input-syntax/INPUT_PW.html#id3775702

More info can be found there in regarding celldm, ibrav, CELL_PARAMETTERS

PS: you should not change subject of your email. This would help to
keep your email in the same thread, and help others to understand well
your situation.
--------------------------------------------------
Duy Le
PhD Candidate
Department of Physics
University of Central Florida.

"Men don't need hand to do things"



On Thu, Aug 4, 2011 at 1:06 PM, dipak thakur <deepak.p.thakur at gmail.com> wrote:
> Sir,
>
> Good evening.
>
> I think I was unable to convey my message correctly.
>
> Kindly go through the input file below.
> ---------------------------------------------------------------------------------------------------------
> ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
>  &CONTROL
>                        title = Graphene mono layer ,
>                  calculation = 'relax' ,
>                 restart_mode = 'from_scratch' ,
>                       outdir = '/root/tmp/' ,
>                   pseudo_dir = '/root/Desktop/QUANTUM_ESPRESSO/pseudo/' ,
>                       prefix = graphene ,
>                      disk_io = 'default' ,
>                    verbosity = 'default' ,
>                etot_conv_thr = 1.D-4 ,
>                forc_conv_thr = 1.D-3 ,
>                        nstep = 50 ,
>                           dt = 40 ,
>  /
>  &SYSTEM
>                        ibrav = 0,
>                    celldm(1) = 1.0000000,
>                    celldm(2) = 1.0000000,
>                    celldm(3) = 0.5000000,
>                          nat = 32,
>                         ntyp = 1,
>                      ecutwfc = 50 ,
>                      ecutrho = 400 ,
>                  occupations = 'smearing' ,
>                     smearing = 'methfessel-paxton' ,
>                        nspin = 1 ,
>                   lda_plus_u = .false. ,
>  /
>  &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
>     16.121319540    9.383047808    0.000000000
>      0.000000000   18.658162370    0.000000000
>      0.000000000    0.000000000   56.689342400
> ATOMIC_SPECIES
>     C   12.01070  C.pbe-van_bm.UPF
> ATOMIC_POSITIONS angstrom
>     C      2.891630000    7.402190000    2.000000000
>     C      3.592920000    8.638320000    2.000000000
>     C      3.603490000    6.167020000    2.000000000
>     C      5.018600000    8.645010000    2.000000000
>     C      5.021500000    6.165980000    2.000000000
>     C      5.733020000    7.405220000    2.000000000
>     C      1.471840000    7.396160000    2.000000000
>     C      2.891120000    9.870660000    2.000000000
>     C      2.894710000    4.932640000    2.000000000
>     C      5.733190000    9.888500000    2.000000000
>     C      5.736430000    4.941300000    2.000000000
>     C      7.163480000    7.412030000    2.000000000
>     C      1.474740000    4.926900000    2.000000000
>     C      0.762281000    8.627830000    2.000000000
>     C      0.763134000    6.161720000    2.000000000
>     C      1.471500000    9.863350000    2.000000000
>     C      3.603410000   11.109500000    2.000000000
>     C      5.021240000   11.123900000    2.000000000
>     C      3.605120000    3.701560000    2.000000000
>     C      5.026450000    3.707890000    2.000000000
>     C      7.878070000    8.655320000    2.000000000
>     C      7.163730000    9.894970000    2.000000000
>     C      7.162030000    4.948140000    2.000000000
>     C      7.876190000    6.176770000    2.000000000
>     C      5.736340000   12.352200000    2.000000000
>     C      0.772689000    3.691020000    2.000000000
>     C      0.762793000    1.220030000    2.000000000
>     C      7.876450000   11.133700000    2.000000000
>     C      7.162030000   12.358700000    2.000000000
>     C      7.872010000   13.592200000    2.000000000
>     C      2.894790000    2.466190000    2.000000000
>     C      1.474820000    2.458780000    2.000000000
> K_POINTS automatic
>   6 6 1   1 1 1
>
> ---------------------------------------------------------------------------------------------------------
> ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
>
> I am desparately trying to understand how to determine:
> 1. The
> CELL_PARAMETERS
>     16.121319540    9.383047808    0.000000000
>      0.000000000   18.658162370    0.000000000
>      0.000000000    0.000000000   56.689342400
> (or how are they determined in this case) - This is again a copy of earlier
> post.
> 2. The          celldm(1) = 1.0000000,
>                    celldm(2) = 1.0000000,
>                    celldm(3) = 0.5000000,
>                    How do I fix them.
> Is there any software and/or technique to do this? or Is there any
> mathematical relation that would be able to provide me these values.
> The cell parameters are given to a precision upto 9th decimal place.
>
> Secondly, the celldm(3) =0.5, does it mean that it would divide the value
> 56.689342400 by 2 and can similar logic be applied to celldm(1) and
> celldm(2)?
> Thirdly, if I view the geometry in XcrySDen, it show vacuum layers in Z
> direction, but no gap/vacuum in x and y direction? I have seen this in many
> papers published till date and is trying to understand these things.
> Doesn't the adjacent supercell (in x and y direction) interact with the
> supercell under consideration?
> Also is there relation between the co-ordinates of the atom, the CELL
> PARAMETERS and celldm()?
>
> I hereby request you to kindly help me in this regard.
>
> Deepak Thakur
> Research Student
> Swami Ramanand Teerth Marathwada University,
> Vishnupuri, Nanded,
> Maharashtra,
> India.
>
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>


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