# [Pw_forum] Turbo TDDFT for a quantum dot

SungHwan Choi sunghwanchoi91 at gmail.com
Sun Jul 24 03:45:00 CEST 2016

Dear Dario,
Thank you for a kind reply. You mean that if it is converged without
smearing option, then there is no problem on doing turboTDDF calculation.
Am I correct?
Sincerely,
Sunghwan Choi

========================================
Sunghwan Choi
Ph.D candidate
Computational Quantum Molecular Science Lab
Department of Chemistry, KAIST, Republic of Korea

2016-07-23 16:43 GMT+09:00 dario rocca <roccad at gmail.com>:

> Dear Sunghwan,
> I have not used the code on systems with the characteristics you describe.
> This is my guess: As far as the ground state of your quantum dot converges
> without a smearing the turboTDDFT code can be used and will be stable.
> While the independent electron polarizability of a 0 gap system diverges
> for \omega-->0, the Hartree part in the TDDFT kernel will increase the
> value of the gap and/or will "push" the oscillator strength to higher
> energies.
> Best,
> Dario
>
>
> On Fri, Jul 22, 2016 at 6:37 PM, SungHwan Choi <sunghwanchoi91 at gmail.com>
> wrote:
>
>> Dear all,
>> I am checking whether turboTDDFT program is suitable for my project. My
>> project is to calculate absorption spectrum of metallic quantum dot. I have
>> two questions.
>>
>> 1) From other post, I read the fact that turboTDDFT cannot calculate a
>> metallic system. Here, how do we define metallic system? just system that
>> have no band gap? then for small metallic quantum dot can be a non-metallic
>> system since it has small band gap (0.1~0.5eV). case that fractional
>> occupation does not happen? then, we can control the occupation parameter
>> not to make fractional occupation.
>>
>> 2) A metallic quantum dot has a size-dependency for band gap. Thus, if
>> size become larger, then band gap become narrow. When turboTDDFT failed to
>> predict an absorption spectrum? and do you know a numerical trend of
>> artifact, which come from low band gap?
>>
>> By the way, does this limit come from algorithm or implementation of
>> turboTDDFT? As far as I understood there is no limit of algorithm itself. I
>> think there is some practical issues on there. Would you tell me where some
>> troubles come up?
>>
>> Sincerely
>> Sunghwan Choi
>>
>>
>> ========================================
>> Sunghwan Choi
>> Ph.D candidate
>> Computational Quantum Molecular Science Lab
>> Department of Chemistry, KAIST, Republic of Korea
>>
>>
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>
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