[DFTB-Plus-User] R: SK files order sensitivity

[Alessandro Pecchia]

Dear Linwei,

X-Y.skf contains all two center integrals of the type
V_s(X)s(Y)_sigma, V_p(X)s(Y)_sigma, V_p(X)p(Y)_sigma, V_p(X)p(Y)_pi, etc...
And Y-X.skf contains integrals like
V_s(Y)s(X)_sigma, V_p(Y)s(X)_sigma, V_p(Y)p(X)_sigma, V_p(Y)s(X)_pi, etc...

In case of Hydrogen, and only because H is (usually) parameterized just with 1 s orbital, we can use the same file. X-H.skf = H-X.skf, since V_s(X)s(H)_sigma = V_s(H)s(X)_sigma. 

Hope this helps

Alessandro 


-----Messaggio originale-----
Da: DFTB-Plus-User [mailto:dftb-plus-user-bounces at mailman.zfn.uni-bremen.de] Per conto di Bálint Aradi via DFTB-Plus-User
Inviato: giovedì 19 marzo 2020 11:26
A: dftb-plus-user at mailman.zfn.uni-bremen.de
Cc: Bálint Aradi
Oggetto: Re: [DFTB-Plus-User] SK files order sensitivity

Dear Linwei,

> Does anyone know the reason for the two files to be different?

Because the X-Y.skf do not contain all integrals between X and Y, just a subset of them. And Y-X.skf contains the other subset. H-X and X-H are special, they should differ, but due to a technical trick, you can the same file for X-H and H-X, provided you take the right one. (Not recommended).

See the documentation on the SK-file format for more details:

http://www.dftb.org/parameters/introduction/

Best regards,

Bálint


--
Dr. Bálint Aradi
Bremen Center for Computational Materials Science, University of Bremen http://www.bccms.uni-bremen.de/cms/people/b-aradi/