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

[Lucas Lodeiro]

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 (<laurens... 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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