[Pw_forum] surface energy convergence for thin films

[Gabriele Sclauzero]

mohnish pandey wrote:
> Dear users!
>                     I am calculating the energy of gallium nitride thin 
> films of thickness of 1-10 layers. I am giving 'nstep'  equal to 200 but 
> the output file is not showing any  message of convergence. The program 
> is just completing the 200 iterations. I have played with all the 

Iterations in the electronic self-consistent loop or iterations (displacements) in the 
ionic trajectory? Be careful that nstep refers to the latter, while electron_maxstep to 
the former.
I suppose you are speaking of the electronic convergence.


> parameters like 'mixing', 'smearing', etc. I am pasting the input file 
> for 9 layer calculation. Can anybody please point out  my mistake and 

Have you tried to converge (in a scf run) the respective bulk phases before starting a 
complicated calculation in a complicated geometry? It' always better start with simple 
things and understand them before moving to more complicated (=interesting) cases.

In you input file I see some problems:
1.Since you are using ultrasoft, you need to specify a meaningful value of ecutrho. Maybe 
you also need to increase ecutwfc.
2.Have you tried to visualize your structure (for instance with xcrysden) to see if all 
atoms are in the right place?
3.Why do you remove symmetry? It usually helps convergence



GS

> get me out of it.
> Sincere Thanks in advance.
> 
> 
>  &control
>     calculation = 'vc-relax',
>     restart_mode='restart',
>     nstep=200,
>     outdir='/home/rajpala/Desktop/wurtzite9',
>     pseudo_dir='/home/rajpala/Desktop/wurtzite9'
>     prefix='gan',
>     tstress = .true.,
>     tprnfor = .true.,
>   /
>   &system   
>     nosym =.TRUE.,ibrav=  4, a = 3.1427, c = 45,nat=  18, ntyp= 2,
>     ecutwfc = 25,occupations='smearing',degauss=.02,smearing='m-v'
>   /
>   &electrons
>    diagonalization='david'
>    mixing_mode = 'local-TF'
>    mixing_beta = 0.1
>    electron_maxstep=200
>    conv_thr = 1.0d-6
>  /
> &IONS
>   ion_dynamics='bfgs'
> /
>  &CELL
>   cell_dynamics='damp-w'
>  /
> ATOMIC_SPECIES
>   Ga 69.723 Ga.pbe-nsp-van.UPF
>   N 14.0067 N.pbe-rrkjus.UPF
>  ATOMIC_POSITIONS (crystal)
>   Ga 0.33333333 0.66666666 0.0577
>   Ga 0.33333333 0.66666666 0.17327
>   Ga 0.00 0.00 0.1154
>   Ga 0.00 0.00 0.23105
>   Ga 0.33333333 0.66666666 0.288
>   Ga 0.00 0.00 0.3459
>   Ga 0.33333333 0.66666666 0.4045
>   Ga 0.00 0.00 0.4623
>   Ga 0.33333333 0.66666666 0.5206
>   N  0.0 0.0 0.0398
>   N  0.0 0.0 0.1553
>   N  0.33333333 0.66666666 0.0957
>   N  0.33333333 0.66666666 0.2130
>   N  0.0 0.0 0.2708
>   N  0.33333333 0.66666666 0.3279
>   N  0.0 0.0 0.3873
>   N  0.33333333 0.66666666 0.4443
>   N  0.0 0.0 0.5035
>  K_POINTS (automatic)
>  6 6 1 0 0 0
> 
> 
> -- 
> Mohnish Pandey
> Y6262,4th Year Undergraduate,
> Department of Chemical Engineering,
> IIT KANPUR
> 
> 
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