[CP2K-user] [CP2K:18008] LR-TDDFT for finite atom probe

[Alex]

Hi Augustin,

You're right. I just had an accompanying discussion regarding X-ray probes, 
hence the casual mentioning of XAS, which indeed would be irrelevant for 
UV. 
That said, the electric field part does bother me. One of the reasons I 
asked about it is that I had issues with boron nitride disintegration under 
a field that was x1000 weaker than what we have here (DFTMD at the PBE-GTH 
level). As soon as the field was removed, the calculations proceeded 
successfully. In any case, it seems like there is a path forward. Thanks a 
lot for your response!

Alex

On Wednesday, November 9, 2022 at 6:56:24 AM UTC-7 Augustin Bussy wrote:

> Hi Alex,
>
> If you are interested in UV absorption spectroscopy, you cannot use the 
> XAS LR-TDDFT method you mention. This method specifically targets core 
> states, and only X-ray photons could excite electrons from these states. 
> The typical energy of UV photons is a few eVs, corresponding to electronic 
> excitations from valence states. For this, standard TDDFT is the 
> appropriate choice. A priori, there is nothing preventing you to run a 
> TDDFT calculation with a strong static electric field.
>
> Best,
>
> Augustin
> On 11/9/22 01:29, Alex wrote:
>
> Hi all, 
>
> I have never done excited-state QC calculations, so I'd like your general 
> input on the basic possibility of getting physically relevant data in our 
> scenario. I have looked at the article on CP2K's XAS LR-TDDFT and I am not 
> entirely convinced there's a path forward. 
>
> What we have is a finite solid tip in the presence of a strong strong 
> (order of tens V/nm) electric field, say, along the tip axis, exposed to a 
> UV pulse. The ultimate goal is to look at "the usual," i.e., maybe electron 
> density distribution & densities of states at the surface/beneath the 
> surface, both in the absence of any pulses, as well as dynamic behaviors 
> upon UV adsorption. In this scenario, I am not convinced that the 
> core-valence separation would be valid, given the polarization under strong 
> static E-field. The tip material is, say, silicon or something similar.
>
> Any comments? Thank you!
>
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>
> -- 
> Augustin Bussy
> Postdoctoral researcher
> Hutter Group
> University of Zurich
>
>

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