[CP2K-user] [CP2K:11065] comparing CP2K-DFTB (5.1) and DFTB+ (18.2)

[Maxime Van den Bossche]

Hi all,

I also did a quick comparison now between CP2K and DFTB+
for a simple rocksalt MgO structure (8 atoms in total,
using the OT minimizer in CP2K). The input and output 
files for both codes are attached. 

What I found so far:

* Without periodicity, the two codes agree quite well
  in terms of the H0 and SCC energies (up to ~1e-4 Ha)
  as well as the Mulliken charges.

* In the periodic case, so far I haven't managed to
  get comparable results with the two codes. The CP2K
  results indeed appear sensitive to the choice of the 
  Ewald alpha parameter, similar to what Wei observed.
  For each of the three ALPHA values I tried, the resulting
  energies and SCC charges are quite different from DFTB+.

* In contrast to Wei, though, I also get different results
  for both codes in non-self-consistent calculations
  (but at least here the CP2K results indeed no longer
  depend on ALPHA).

It would be great if you could check whether my CP2K
inputs have been appropriate. If so, I hope this example will
help to get to the bottom of this.

Best,
Maxime
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