[Pw_forum] Help regarding supercell

[dipak thakur]

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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