[Pw_forum] ph.x can only address LDA potentials? (Gabriele Sclauzero)

[Eyvaz Isaev]

Hi,

--- On Fri, 8/28/09, 刘永铎 <liuyongduo at hotmail.com> wrote:

> But the result is very bad-20% higher than the experimental
> one..
 
Which one is higher? Sometime 20% error looks acceptable,  

> Any body who have done Raman spectra can give me some help?

The message from phq_setup.f90 is:
'third order derivatives not implemented with GGA'

Well, you try to calculate the Raman activity in SiH4, most likely via QE 4.1. The message (and immediate stop) appeared in this version, but it is absent in previous versions  up to 4.0.5. But not sure the result will be correct (with versions <=4.0.5). The restriction might be due to complex integrals within GGA.

Did you try US+LDA?

Bests,
Eyvaz.

-------------------------------------------------------------------
Prof. Eyvaz Isaev, 
Theoretical Physics Department, Moscow State Institute of Steel & Alloys, Russia, 
Department of Physics, Chemistry, and Biology (IFM), Linkoping University, Sweden 
Condensed Matter Theory Group, Uppsala University, Sweden 
Eyvaz.Isaev at fysik.uu.se, isaev at ifm.liu.se, eyvaz_isaev at yahoo.com




> 
> but I've already tried Ultra soft or some other forms
> of GGA, and it seems that the third derivative of energy is
> not yet implemented for USpps or GGA.(I forgot the exact
> error messages)
> 
> For SiH4, the energy w.r.t any possible parameter converge
> very well. The cutoff I am using is 70ry which is more than
> enough actually for that potential (Si.pz-vbc.UPS)
> Since the SiH4 is in gas phase, so I used a big box to put
> the SiH4. So no worry about the lattice parameters.
> 
> But the result is very bad-20% higher than the experimental
> one..
> 
> Any body who have done Raman spectra can give me some help?
> (badly needed)
> 
> 
> best 
> 
> 
> Yongduo Liu
> 
> University of California, Los Angeles
> Materials Science and Engineering 
> 
> 310-467-8389
> 
> 
> > 
> > Message: 1
> > Date: Fri, 28 Aug 2009 08:56:57 +0200
> > From: Gabriele Sclauzero <sclauzer at sissa.it>
> > Subject: Re: [Pw_forum] ph.x can only address LDA
> potentials?
> > To: PWSCF Forum <pw_forum at pwscf.org>
> > Message-ID: <4A977FB9.7070002 at sissa.it>
> > Content-Type: text/plain; charset=UTF-8;
> format=flowed
> > 
> > Dear pw user,
> > 
> > ??? wrote:
> > > Dear Pw user:
> > > 
> > > 
> > >      I am trying to calculate Raman spectrum of
> some stuff. But it seems 
> > > that the ph.x complains whenever I use potentials
> other than LDA. It 
> > > gives error messages like:
> > >   
> > >     * The phonon code with ### and raman, elop or
> elph is not yet 
> > > available.*
> > 
> > What are you hiding under ###? The only error message
> that I could find in the ph.x 
> > sources and can match yours is:
> > 
> >
> [sclauzer at brenta:/scratch/sclauzer-exec/espresso-4.1/PH]$
> grep available *.f90
> > ...
> > phq_readin.f90:     'The phonon code with paw and
> raman, elop or elph is not yet available',1)
> > ...
> > 
> > This message does not mean that you cannot use any DFT
> functional other than LDA, but that 
> > you cannot use PAW together with Raman or El-Ph
> coupling calculations for instance. You 
> > can always use ultrasoft pseudopotentials (US-PPs)
> instead of projector augmented waves, 
> > and I think that with US PPs there are no such
> limitations. For PAW, well you may have to 
> > wait some time, or think about implementing it
> yourself and then contributing it to the 
> > community.
> > 
> > 
> > >  
> > >      So, is the lda-potentail our only choice?  
> But the calculated 
> > > Raman mode is very bad comparative to the
> experimental results. For 
> > > instance, SiH4, it gives:
> > > 
> > > #  mode   [cm-1]     [THz]      IR          
> Raman     depol
> > >     1      0.00    0.0000    0.0000        
> 0.0791    0.7500
> > >     2      0.00    0.0000    0.0000        
> 0.1194    0.7500
> > >     3      0.00    0.0000    0.0000        
> 0.0679    0.7500
> > >     4      0.00    0.0000    0.0000        
> 0.0970    0.7500
> > >     5      0.00    0.0000    0.0000        
> 0.0051    0.7500
> > >     6      0.00    0.0000    0.0000        
> 0.0235    0.7500
> > >     7    634.67   19.0268    1.0902        
> 1.1145    0.7500
> > >     8    634.67   19.0268    1.0902        
> 1.1145    0.7500
> > >     9    634.67   19.0268    1.0902        
> 1.1145    0.7500
> > >    10    819.69   24.5735    0.0000        
> 8.4725    0.7500
> > >    11    819.69   24.5735    0.0000        
> 8.4725    0.7500
> > > *   12   2524.31   75.6765    0.0000      
> 267.0683    0.0000*    ? this 
> > > one?
> > >    13   2546.65   76.3462    3.3789       
> 81.6301    0.7500
> > >    14   2546.65   76.3462    3.3789       
> 81.6301    0.7500
> > >    15   2546.65   76.3462    3.3789       
> 81.6301    0.7500
> > > 
> > > 
> > > but the experimental value is 2187 cm-1
> > 
> > It may be that LDA overestimates a frequency. Anyway,
> are you sure you converged with 
> > respect to all relevant parameters, cut-offs,...? What
> is the lattice parameter you used? 
> > ...?
> > 
> > regards,
> > 
> > Gabriele
> > 
> > 
> > > 
> > > 
> > > best
> > > 
> > > 
> > > Yongduo
> > > 
> 
> 
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