[DFTB-Plus-User] Energy difference between DFTB3 or SCC-DFTB with HF or CCSD(T)

prasantb prasantb at iitk.ac.in
Tue Sep 14 11:11:38 CEST 2021


Hi community members,

I have just ran my first few test calculations with DFTB+. I have found 
a page for some test calculations, 
https://dftbplus-recipes.readthedocs.io/en/latest/basics/firstcalc.html#band-out. 
 From there I ran water molecule optimization. I ran that and found that 
the Total energy is -4.0618820527 H. However, the HF or CCSD(T) 
calculation shows the total energy to be ~-76 Hartree. I know that DFTB 
can not give same energy with HF but this is a rather large deviation.

What is the problem or what am I missing here?

-- 
Thanking You,
Prasanta Bandyopadhyay
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