LR-TDDFT for finite atom probe

[Alex]

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!

[Augustin Bussy]

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

--
You received this message because you are subscribed to the Google Groups "cp2k" group.
To unsubscribe from this group and stop receiving emails from it, send an email to cp2k+uns...@googlegroups.com.
To view this discussion on the web visit https://groups.google.com/d/msgid/cp2k/2ffb32e3-1619-4b91-828e-00db37b64142n%40googlegroups.com.

-- 
Augustin Bussy
Postdoctoral researcher
Hutter Group
University of Zurich

[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