[Pw_forum] supercell question

[James Johns]

Hi Sara,
  It looks like you made a supercell with 5 layers in your input, and a
vacuum of 3*7.56 bohr.  I loaded it up in xcrysden just to check, so I'm
not sure what the trouble is.  If you wanted to increase the number of
layers, you could continue to add copper atoms to your atomic positions at
z=1.5, 2, 2.5 etc as.  You could increase the size of your vacuum by
increasing celldm(3) as well.  As long as you keep your atomic positions in
alat you should be good to go.
Let me know if that helps,
James

On Wed, Feb 10, 2016 at 8:17 AM, Sarah Alpine <sarahalpine1 at gmail.com>
wrote:

> Dear Users,
>
>      I would really appreciate some advice, please. I would like to model
> 6-7 layers of copper, and 2-3 layers of titanium dioxide. Since it is a
> film, I also need to add vacuum to this supercell. I am starting out with
> just the copper; I wrote the coordinates of the unit cell, how do I create
> 6-7 layers for the supercell with vacuum rather than create a crystall out
> of the unit cell?
> Thanks,
> Sarah
>
> &control
>     calculation='scf'
>     pseudo_dir = '../espresso/pseudo/',
>     outdir='./TMP/'
>     prefix='copper001'
>  /
>  &system
>     ibrav = 6, celldm(1) =7.56, celldm(3)=5.0, nat= 10, ntyp= 1,
>     ecutwfc = 30.0, ecutrho = 240.0
>     occupations='smearing', smearing='marzari-vanderbilt', degauss=0.02
>  /
>  &electrons
>     diagonalization='david'
>     conv_thr = 1.0e-7
>     mixing_beta = 0.7
>  /
> ATOMIC_SPECIES
>  Cu 63.55 Cu.pbe-nd-rrkjus.UPF
> ATOMIC_POSITIONS alat
> Cu 0.0 0.0  1.0
> Cu 0.5 0.5  1.0
> Cu 0.5 0.0  0.5
> Cu 0.0 0.5  0.5
> Cu 0.0 0.0  0.0
> Cu 0.5 0.5  0.0
> Cu 0.5 0.0 -0.5
> Cu 0.0 0.5 -0.5
> Cu 0.0 0.0 -1.0
> Cu 0.5 0.5 -1.0
> K_POINTS (automatic)
>  8 8 8 1 1 0
>
>
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-- 
James E. Johns
Assistant Professor
Department of Chemistry
University of Minnesota
207 Pleasant St.
Minneapolis, MN 55455
http://www.chem.umn.edu/groups/johns/index.html
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