[Pw_forum] Strange Values of Tc

[Warren Pickett]

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
>
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