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

[刘永铎]

Thank you very much!

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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