DFTB3 and DFTB-D3

[Linc]

Dear CP2K developers/users,

I noticed that since version 2.6 CP2K has incorporated the 3rd order 
correction to DFTB and also included the D3 dispersion corrections. Just to 
make sure I understand the implementation correctly, I wish to ask the 
following two questions.

(1) The function for damping hydrogen bonds takes the form of exp[ 
-((U_a+U_b)/2)^HB_SR_PARAM * r_ab ]. If I want to use the 3OB Slater-Koster 
files, then HB_SR_PARAM should be 4.0 as specified by the 3OB parameter 
set. But, the question is: if/how can I define the Hubbard parameters U_a 
and U_b? I guess CP2K has default values for them, but would it be possible 
to specify them by the user? FYI, Eq. 7 in J. Chem. Theory Comput., 2013, 9 
(1), pp 338.

(1) Regarding the D3 corrections for DFTB, can I assume that the dftd3.dat 
file, provided under ./cp2k-2.6.0/data/, contain the DFTB-compatible 
parameters as used by S. Grimme in J. Phys. Chem. Lett., 2014, 5 (11), pp 
1785 (if there are such parameters at all - sorry, haven't gone through all 
the relevant literature). 

Many thanks in advance for any information/help on these questions!

Best regards,
Linc
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