[CP2K-user] [CP2K:15030] Bulk Silicon Tddft

[Matt W]

Yes, this is likely the problem. I don't think TDDFT with smearing has been 
tested / considered.

On Monday, March 29, 2021 at 4:33:38 PM UTC+1 Lucas Lodeiro wrote:

> Hi,
>
> I am not an experto on TDDFT, but seeing your output there is something 
> suspicious. For TD1 you have 4 states occupied (thinking in the 0K 
> electronic structure), and correctly the TDDFT transitions occur from these 
> 4 occupied states to the virtual states in the "Gamma Point". But when you 
> double (or higher) the cell, the excitations occur from states over the 
> occupied states. For example in TD2: 32 occupied states, and the lower 
> citations occur from 38... the same occur for TD3, TD4, TD5.
> It seems that the smearing pumps fractions of electrons to virtual states, 
> and the program assumes that virtual-low populated states are 
> occupied states.
> If this is the problem, you can solve it by removing the smearing... Si is 
> a semiconductor, and without smearing is possible to compute it electronic 
> structure.
>
> Regards
>
> El lun, 29 mar 2021 a las 10:10, Laurens (<lau... at msn.com>) escribió:
>
>> Dear all,
>>
>> I am trying to do tddft simulations of bulk silicon (please see attached 
>> band structure and in/output files).
>>
>> Since tddft is not implemented for k-points, I have tried using 
>> supercells of sizes up to and including 5x5x5 times the primitive unit cell.
>> This changes the lowest excitation energy, but unfortunately the lowest 
>> excitation energy does not seem to converge to a value close to the 
>> calculated bandgap of 0.7 eV: the lowest excitation energy decreases from 
>> an energy of 2.2 eV for the single unit cell, to an energy between 0.28 eV 
>> (4x4x4 cell) and 0.85 eV (3x3x3 cell).
>>
>> Does anybody have any suggestions on tddft simulations of bulk solids?
>>
>> Best regards,
>>
>> Laurens
>>
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