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

[Giuseppe Mattioli]

Dear Pablo

> 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?

You still have a vague idea of what is a plane wave basis set for ab initio calculations... :-)
The brute answer to your question is: increase separately ecutwfc and ecutrho until a given parameter of your calculation (total energy, lattice 
parameters, forces on atoms, whatever...) becomes stationary within an arbitrary range of values, let us say, for instance, 0.001 Ry in the case of 
total energy. Of course there are common ranges of ecutwfc and ecutrho values usually suitable for a given kind of calculation, and they depend 
(mainly) on the pseudopotentials used in such calculation. You *should not* perform plane-wave calculations if you don't know (possibly quite well) 
what is a pseudopotential and which are the theoretical and practical differences between the ultrasoft, norm-conserving and PAW approaches. You may 
start from this treasure "hidden" in the QE distribution :-)

YourEspresso/5.1/atomic/Doc/pseudo-gen.pdf

and from all the references cited therein.

HTH

Giuseppe

On Thursday, November 27, 2014 12:49:13 AM pablohi wrote:
> 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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> ********************************************************
> 
>   Giuseppe Mattioli
> 
>   CNR - ISTITUTO DI STRUTTURA DELLA MATERIA
> 
>   v. Salaria Km 29,300 - C.P. 10
> 
>   I 00015 - Monterotondo Stazione (RM)
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********************************************************
- Article premier - Les hommes naissent et demeurent
libres et ègaux en droits. Les distinctions sociales
ne peuvent être fondèes que sur l'utilitè commune
- Article 2 - Le but de toute association politique
est la conservation des droits naturels et 
imprescriptibles de l'homme. Ces droits sont la libertè,
la propriètè, la sùretè et la rèsistance à l'oppression.
********************************************************

   Giuseppe Mattioli                            
   CNR - ISTITUTO DI STRUTTURA DELLA MATERIA   
   v. Salaria Km 29,300 - C.P. 10                
   I 00015 - Monterotondo Stazione (RM)          
   Tel + 39 06 90672836 - Fax +39 06 90672316    
   E-mail: <giuseppe.mattioli at ism.cnr.it>
   http://www.ism.cnr.it/english/staff/mattiolig
   ResearcherID: F-6308-2012