[Pw_forum] Phonon at q=0

[mayank gupta]

Thanks Sir for your response.

I am doing all these calculations for oxides. for example I have done
the phonon calculations for Cu2O and Ag2O system the details are as
follow

Ag2O ecutwfc 70 Ry.  Mesh  (8x8x8)        zone ceneter acoustic
mode=1.6 THz (with PBE)
Cu2O ecutwfc  95 Ry. Mesh  (8x8x8)        zone centre acoustic mode =
1.33 THz (PW)

I have performed above calculation using tr2_ph=1.0e-14, but the
values are almost same. the ecutrho=20times of ecutwfc.


Mayank


> Dear Mayanka,
>
> is this a polar material? If so, the violation of the ASR may be justified
> by the use of too coarse a k-point mesh. Please, provide more details on the
> system and the calculations you are doing.
>
> SB
>
> On Jul 1, 2011, at 6:17 AM, mayank gupta wrote:
>
>> Dear All
>> I have a query ragrdin phonon calculations at q=0. When I performed
>> the phonon caclualtion at q=0, we didn't get zero enrgy for acoustic
>> branches, however they can be set to zero by using acoustic/ crystal
>> sum rules. My question is if the zone center acoustic braches values
>> are too large (4 THz) even we have implemented very high convergence,
>> it is ok to apply ASR.
>>
>> Thanks
>>
>> --
>> Mayank


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