1) Why didn't you include D3 or
D4 corrections in your first calculation? I might be wrong, but
dispersion corrections will improve geometries in most cases, if not
all.
2) Why use ORCA 5.0.3 when version 5.0.4 has been out for quite
some time now, and many bugs were corrected or
detected?
Regarding the use of D4 in ORCA, in the release
notes for version 5.0.3, the first post in the ORCA forum
says:
"Unfortunately, the C++ implementation of
the DFT-D4 code was affected by a bug in the gradient and some further minor
bugs.
This affects all DFT gradient (and thus also hessian) calculations
using D4 in ORCA mainly manifesting in sometimes erroneous geometry
optimizations.
In most cases this breakdown is indicated by geometry
optimizations running up in energy/gradient. The magnitude of the error is not
generally assessable and should be checked for each individual case (it can be
negligibly small for many systems). In any case, it is recommended to check the
convergence behavior/final geometry in comparison to a D3
calculation.
Further, some elements (Li, Be, Na, Mg, K, Ca, Sc, Ti, V,
Rb, Sr, Y, Zr, Nb, Cs, Ba, Hf, Ta) did not make use of the revised reference
polarizabilities given in DOI: 10.1039/D0CP00502A resulting in minor energy
differences compared to the current DFT-D4 standalone code provided by Grimme
and co-workers.
These bugs also affect the r2SCAN-3c composite method.
D3, GFN-xTB and GFN-FF methods are NOT affected!
In any case, all
energies computed with the ORCA implementation of D4 should be checked with the
stand alone code (current stable release version 3.5.0,
https://github.com/dftd4/dftd4).
The bug will be fixed in the
upcoming ORCA 5.0.4 release.
The Grimme Group DevTeam & ORCA
Team"
It may be advisable to re-run these
calculations with version 5.0.4 using D3 or D4 corrections, checking if you get
the same problems.