[Pw_forum] Fwd: Re: Fwd: Re: parameteres of quantum dots

[pablohi]

Thanks for your help!

I'm learning this by my own in order to do my master thesis. I didn't 
choose the atom positions, my supervisors did it for me. I have read a 
few articles these two days and know I have things more clear. My last 
doubt is about The energy cutoff I have to choose. The total energy of 
my system is about 340000 ry. The question is: Shall i used a energy 
cutoff of 300.0 ry or so?

Thanks in advance, your help was very usefull for me!

Regards

Pablo Hidalgo Romera
Computer architecture and electronics department(student)
University of Granada(Spain)

-------- Mensaje original --------
Asunto: Re: [Pw_forum] Fwd: Re:  parameteres of quantum dots
Fecha: 2014-11-24 11:34
Remitente: Giuseppe Mattioli <giuseppe.mattioli at ism.cnr.it>
Destinatario: PWSCF Forum <pw_forum at pwscf.org>
Respuesta a: PWSCF Forum <pw_forum at pwscf.org>



Dear Pablo

It seems that you are attempting to perform complex calculations 
without
going through a proper training and without supervision. There are
several critical issues in your input file, and this forum is generally
not intended for training. I can only point out the bad mistakes, but
you should take your time to learn the hard way...

> I want to simulate the energies spectrum of CdSe Quantum Dots

What is it? Are you talking about optical absorption spectrum? Are you
aware of the difference between DFT and TD-DFT?

>      ibrav = 0,

> CELL_PARAMETERS {bohr}

>

>    32.5033024000     0.0000000000     0.0000000000

>    -16.2516512000    28.1486855853     0.0000000000

>      0.0000000000     0.0000000000    39.8082529177

why a monoclinic cell?

>      ecutwfc = 10.0,ecutrho = 80.0,

poorly unconverged plane wave basis set

> ATOMIC_POSITIONS  {bohr}

find attached an image representing your system, as obtained by opening
your input with xcrysden. There is clearly something wrong, and apart
from the position of H atoms, too close to the Cd and Se atoms, the
structure seems to be the right one. A hint: look for the options of
ATOMIC_POSITIONS in the pw.x manual.

>      occupations='smearing', smearing='marzari-vanderbilt',
degauss=0.05

Is your system a metal?

>      noncolin = .false.

useless

>     calculation='bands'

why do you need it?

HTH

Giuseppe

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