[Pw_forum] ph.x can only address LDA potentials?

[Gabriele Sclauzero]

Dear pw user,

刘永铎 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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-- 


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| Gabriele Sclauzero, PhD Student                  |
| c/o:   SISSA & CNR-INFM Democritos,              |
|        via Beirut 2-4, 34014 Trieste (Italy)     |
| email: sclauzer at sissa.it                         |
| phone: +39 040 3787 511                          |
| skype: gurlonotturno                             |
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