[Pw_forum] Regarding supercell dimensions

[dipak thakur]

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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