[Pw_forum] Strange Values of Tc

[Isaiah Moses]

Dear Prof Warren,

Yes, QE uses the Allen-Dynes equation to determine the Tc.

I appreciate your additional insight in to the value of lambda.

We're reexamining to ensure that computational errors and noises are ruled
out.

Then conclusive inference can be made from the result.

Your response is really appreciated.

Isaiah.

On Fri, Jul 28, 2017 at 3:18 PM, Warren Pickett <wepickett at ucdavis.edu>
wrote:

> Isaiah,
>
> I'm not familiar with  the workings of QE, but without solution of the
> full Eliashberg equations it must be using the Allen-Dynes equation (as
> most do) to obtain Tc.
>
> The basic fact is that with a  standard Coulomb repulsion mu-star =
> 0.10-0.15, with lambda less than 0.3 or so there will be no
> superconductivity. The A-D equation was not fit to tiny values of Tc and no
> one should be interested in those results. If non-zero, they will be
> extremely sensitive to lambda, as you can see. [And  you can get
> nonsensical large values! as you can see]
>
> So just accept that if lambda < 0.3 or so, any results cannot be trusted
> and its not an interesting el-ph superconductor.
>
> Warren
>
>
> Warren E. Pickett
> Distinguished Professor of Physics
> Department of Physics
> University of California Davis
> Davis CA 95616, USA
>   Cell: 530-220-2138
>
> On Fri, Jul 28, 2017 at 12:24 AM, Isaiah Moses <imoses87 at gmail.com> wrote:
>
>> Dear everyone,
>>
>> I did an el-ph calculation of a monoclinic structure and am getting
>> really strange values of Tc . See the result below
>> lambda        omega_log          T_c
>>    0.00994       112.048            0.10012314E+08
>>    0.03760        92.373            0.13380511E+10
>>    0.07564        90.247            0.39802174E+19
>>    0.09959        89.414            0.19865362E+78
>>    0.11010        89.463            0.40671597-151
>>    0.11454        90.329            0.16986711E-65
>>    0.11678        92.320            0.99512429E-51
>>    0.11772        94.657            0.29927798E-46
>>    0.11744        97.141            0.16242032E-47
>>    0.11619        99.442            0.65514785E-54
>>
>> I'm wondering why such values.
>>
>> Any comment shall be greatly appreciated.
>>
>> Thanks,
>> Isaiah
>>
>> --
>> Isaiah Abu Moses
>> Graduate Student,
>> Physics Department,
>> University of Ibadan,
>> Nigeria
>>
>> _______________________________________________
>> Pw_forum mailing list
>> Pw_forum at pwscf.org
>> http://pwscf.org/mailman/listinfo/pw_forum
>>
>
>
> _______________________________________________
> Pw_forum mailing list
> Pw_forum at pwscf.org
> http://pwscf.org/mailman/listinfo/pw_forum
>



-- 
Isaiah Abu Moses
Graduate Student,
Physics Department,
University of Ibadan,
Nigeria
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.quantum-espresso.org/pipermail/users/attachments/20170728/35264879/attachment.html>