[CP2K-user] [CP2K:11082] comparing CP2K-DFTB (5.1) and DFTB+ (18.2)

[Wei Lai]

With the intention to help with the discussion, I took the liberty to post
the following numbers.

If I turn off “minimum image convention” or “mic” in qs_neighbor_lists.F
(version 5.1; this was done automatically in version 6.1), the periodic
nonscc results of cp2k are close to those from dftb+.

nonscc total energy:  -14.90396117681518 (cp2k) vs -14.9042897104 (dftb+).

Maxime was using 6.0 development version and the nonscc total energy
was -15.00558399676375.

However, the difference in the periodic scc case became more dramatic:

core energy: -14.7017837002 (dftb+), -11.35591447406040 (cp2k, alpha=0.3),
-13.03486875813706 (cp2k, alpha=0.5), -13.89182287767537 (Maxime, alpha=0.3)
scc energy:  1.2109415266 (dftb+), 2.94796400907580 (cp2k, alpha=0.3),
2.06305475569169 (cp2k, alpha=0.5), 0.07851968376930 (Maxime, alpha=0.3)

Thanks, Wei


On Mon, Dec 24, 2018 at 6:08 AM Thomas Kühne <tku... at gmail.com> wrote:

> Dear Maxime,
>
> your input files looks good to me.
> How large is the difference in the
> periodic cases?
>
> Merry Christmas,
> Thomas
>
> Am 22.12.2018 um 22:45 schrieb Maxime Van den Bossche <
> maxime.cp.v... at gmail.com>:
>
> 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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