[Pw_forum] Fail to predict semiconductor

[Iwan Darmadi]

Dear Mr. Jose,


Thanks for your detail explanation. I'll try to use hybrid function as you suggest. I'll update the results asap.


Sincerely yours,


Iwan D.

 
***

Iwan Darmadi
 Undergrad.Student - Department of Physics

 Universitas Indonesia


________________________________
 From: ""José C. Conesa"" <jcconesa at icp.csic.es>
To: Iwan Darmadi <iwan_darmadi at rocketmail.com> 
Cc: PWSCF Forum <pw_forum at pwscf.org> 
Sent: Friday, January 25, 2013 6:31 PM
Subject: Re: [Pw_forum] Fail to predict semiconductor
 

Dear Iwan,
In the paper you quote, the Ti:ZnO case has the Ti levels inside the
    ZnO conduction band (see fig. 2) - and this even though the latter
    band has been pushed up by applying an ad hoc shift to the Zn 4s
    levels, so that the correct gap of ZnO is obtained. Thus it does not
    seem that the calculation reported there predicts this system to be
    a semiconductor. Of course, experimentally it may happen that the
    material prepared, especially if it was made in even mildly
    oxidizing environment, contains cation vacancies, possibly located
    close to the Ti atoms (assuming these to be at tetrahedral sites -
    which is not a preferred coordination for Ti) so that it could
    behave as semiconductor.
In any case computing correctly band gaps and level positions in
    these systems is tricky even with post-DFT treatments. I try to
    avoid if possible DFT+U (treating differently different electrons is
    not very elegant), and to use hybrids instead. One problem with the
    latter is that the fraction of Fock exchange to be used can be
    questioned. Indeed one same fraction is not valid for both TiO2 and
    ZnO. You can approach the situation better if that fraction is tuned
    to the dielectric constant of the material. If you are interested in
    this specific issue I invite you to look at my recent papers J. Phys. Chem. C116 (2012) 18884  and Catal. Today in press (doi:  10.1016/j.cattod.2012.08.039)  where this solution is explained better, although its suitability for possibly metallic systems like yours can be questioned as well.
Regards,
José-Carlos

 
El 23/01/2013 15:56, Iwan Darmadi escribió:

 Dear Mr.Jose,
>
>
>Yes, I do. But, as far as I know, transition metal doped zno is semiconductor even theoretically (according for example PRB 79/165202 and ). So I assumed that without cation vacancy, Ti doped ZnO might be semiconductor also.
>
>
>Regards,
>ID
>***
>
>Iwan Darmadi
> Undergrad.Student - Department of Physics
>
> Universitas Indonesia
>
>
>
>________________________________
> From: Jose C. Conesa <jcconesa at icp.csic.es>
>To: Iwan Darmadi <iwan_darmadi at rocketmail.com>; PWSCF Forum <pw_forum at pwscf.org> 
>Sent: Wednesday, January 23, 2013 3:09 PM
>Subject: Re: [Pw_forum] Fail to predict semiconductor
> 
>
>Dear Iwan,
>Do you know whether the experimentally
                              known Ti doped ZnO contains cation
                              vacancies?
>Good luck,
>José Carlos
>
>El 23/01/2013 6:50, Iwan Darmadi escribió:
>
>Dear all,
>>
>>
>>
>>I have calculated electronic structure of Ti doped ZnO in both GGA and GGA+U scheme. Both scheme predicts Ti doped ZnO is metallic. In contrary, Ti doped ZnO is well known as semiconductor experimentally. At first glance, I thought it was local minimum problem of DFT+U (like FeO problem in Mr. Himmetoglu's tutorial). Then I try to copy Mr. Himmetoglu's trick to override a "suspected" fully occupied orbitals of Ti. Sadly, nothing change,  it's still a metallic.
>>
>>
>>
>>Now, I am confused whether this is a really local minimum problem or intrinsic limitation of DFT it self.
>>
>>
>>
>>Do anyone here have suggestions so I can get semiconductor Ti doped ZnO in the calculation ?
>>
>>
>>
>>Ps.
>>
>>I have also attached my input and output file.
>>
>>***
>>
>>Iwan Darmadi
>> Undergrad.Student - Department of Physics
>>
>> Universitas Indonesia
>>
>>
>>
>>_______________________________________________
Pw_forum mailing list Pw_forum at pwscf.org http://pwscf.org/mailman/listinfo/pw_forum
>
>
>-- 
José C. Conesa
Instituto de Catálisis y Petroleoquímica, CSIC
Marie Curie 2, Cantoblanco
28049 Madrid - Spain
Tel. +34-915854766
>
>

-- 
José C. Conesa
Instituto de Catálisis y Petroleoquímica, CSIC
Marie Curie 2, Cantoblanco
28049 Madrid - Spain
Tel. +34-915854766 
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