[Pw_forum] Fail to predict semiconductor

[Alexey Akimov]

Dear Iwan,

The pure DFT is known to underestimate the band gaps, eventually making semiconductor material to appear as a metal in your calculations. This problem arises because of the double-counting in exchange terms. The problem solved with the hybrid functionals, such as PBE0. The GGA approximation and even +U correction terms provide only small improvement over LDA. So this may not be enough to make your system to be semiconductor (computationally). To summarize,the problem is inherently with the DFT methododology.

Good luck,
Alexey

----- Original Message -----
From: "Iwan Darmadi" <iwan_darmadi at rocketmail.com>
To: "pw forum" <pw_forum at pwscf.org>
Sent: Wednesday, January 23, 2013 12:50:35 AM
Subject: [Pw_forum] Fail to predict semiconductor







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 

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-- 
Dr. Alexey V. Akimov

Postdoctoral Research Associate
Department of Chemistry
University of Rochester

aakimov at z.rochester.edu