[Pw_forum] Can xpectra.x calculate XAS for metal?

[程迎春]

Dear Guido Fratesi,
Thank you so much for the explaination.
Now I understand how to calculate the xas for the metalic system.
Best, Cheng

2012/6/27 Guido Fratesi <fratesi at mater.unimib.it>:
> Dear Cheng,
>
> xspectra can handle metal systems: see for example PHYSICAL REVIEW B 80,
> 075102 (2009) fig.3.
>
> The Fermi level is taken as the zero of the spectrum, and might be used
> to cut and remove the spectrum below E_F. By editing the value of ef_r
> in input you should obtain the same spectrum, only shifted at different
> energies.
>
> What is the Fermi level for your insulator? Notice, it will depend on
> the choice of occupation functions. So, probably xspectra was giving you
> the HOMO, while if you set smearing with gaussian functions you will get
> something close to (HOMO+LUMO)/2 (depending on occupied/empty DOSs).
> Indeed your E_F in this case is higher. In principle, for systems at
> T=0, anything in between the HOMO and the LUMO is reasonable. The
> resulting spectrum will not change but for the reference energy, it
> suffices that you do things consistently.
>
> Hope this helps,
> Guido
>
> On 06/26/2012 03:25 PM, 程迎春 wrote:
>> Dear all,
>> I have installed QE5.0 with xpectra installed.
>> I just tested the diamond example and it runs through.
>> In this example, the diamond is treated as insulator.(Of course!)
>> In the second step, xspectra.x can get the Fermi level of 0.94038144
>> Ry (12.8 eV).
>> If I set the system as metal with occupation "smearing", the
>> xspectra.x will complained when I try to get the Fermi level.
>> The error message is as below:
>>   Metallic case
>>
>>
>>   %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
>>       from input : error #         1
>>       Read fermi level from scf/nscf output
>>   %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
>>
>>       stopping ...
>>
>> But the Fermi level printed in the scf output file is 15.88 eV.
>> My first question is why the two fermi level value are different so much.
>> Second question is whether xspectra.x can calculate the XAS for metalic system?
>> Thank you in advance.
>> Best,
>>
>
> --
> Guido Fratesi
>
> Dipartimento di Scienza dei Materiali
> Universita` degli Studi di Milano-Bicocca
> via Cozzi 53, 20125 Milano, Italy
>
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-- 
Y. C. Cheng
Department of Physics
Nanjing University
Nanjing 210093
P. R. China
Tel: 86-25-83592907
Email: yccheng.nju at gmail.com