[DFTB-Plus-User] About OB2 parameters and onsite constants

[Bálint Aradi]

Dear In Seong Lee,

> In mio parameter sets (C-H.skf), the values for interaction (sp\sigma of
> H0 and S) between p orbital of C atom and s orbital of H atom exist.
> While those values in ob2 parameter sets (C-H.skf) does not exist, which
> indicate that all values are zero at all distances.

The spurious values in the C-H in mio comes from "lazyness". When people
generated every SK-table by hand, they spared to generate X-H and used
H-X instead (or the otherway around). This trick works due to some
redundancy in the X-Y and Y-X SK-files, but only, if one of the atoms
has an "s"-orbital only. The superfluous data is simple ignored by DFTB+.

When parameters are generated with the newer toolchain
(https://github.com/dftbplus/skprogs/), all files are generated without
"shortcuts". This is why you don't see it in the newer sets.

> Is this correct result? Or Do this have some errors?
> I am not sure, but the molecular orbitals obtained from both sets show
> different phase of H atom.

Phases are not really relevant, as long as they are consistent within
one SK-set.

> 2. Is there onsite constants computed from range-separated functional?
> In DFTB+ manual (20.2 ver), the values obtained from PBE functional only
> exist, thus I want to know the constants with range-separated functional
> if exists.

No, currently we don't have the on-site values with hybrid yet, sorry.


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/


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