[CP2K-user] [CP2K:19103] Re: No agreement between the LR and RT absorption spectra

[Beliz Sertcan]

Hello Natalia,

Regarding the mismatch between CP2K and Gaussian TDDFT results, once should 
use the TDA keyword in Gaussian instead of TD to get an exact match as CP2K 
employs the Tamm-Dancoff approximation. Furthermore, I would highly 
recommend turning on the Poisson section and setting the solver to MT 
instead of analytical.

    &POISSON

       PERIODIC NONE

       POISSON_SOLVER MT

    &END

Since you are working with a heavy element I would also consider using a 
bigger basis such as TZVP maybe even TZV2P. With these additions I think 
you will be able to match the RTP spectrum better, but I would not expect a 
perfect match. In my opinion what you have with the positions of the sticks 
is not so bad.

Best,
Beliz


On Monday, 10 July 2023 at 10:55:39 UTC+2 Natalia K wrote:

Dear community,

I am calculating the absorption spectra for a silver chain using both 
linear response (TDDFPT) and real-time propagation implemented in CP2K 9.1. 
Within the RT propagation, I apply a delta kick in all three directions and 
then take the Fourier transform of the dipole moment and get the average 
(over three directions) spectrum that is in a very good agreement with the 
literature. In particular, with another GGA linear-response calculation 
with the Gaussian code (image attached, top - my results, bottom - 
reference). Within the TDDFPT approach, I calculate the oscillator strength 
which should give the same frequencies as the real-time approach, but it 
doesn't. In the figure attached, the oscillator strength is plotted with 
impulses. I tested many different parameters but LR never agrees with RT. I 
also tested a simpler system, a water molecule, and got a better agreement 
between the two methods, but still not as perfect as here, for instance: 
https://nwchemgit.github.io/RT-TDDFT.html#absorption-spectrum-of-water

I would appreciate any help or suggestion. I attach both RT and LR input 
files used to obtain the results on the figure.

Best regards,

Natalia

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