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Problem with geometry optimization

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1 week 6 days ago #971 by bakowies
Dear all,

I experienced problems with the geometry optimization of
a simple molecule, allene. They happened for DFT and HF and
various basis sets. So to exclude problems with density
integration and keep things simple, I show results only for
HF/3-21G, limiting the number of optimization cycles to 10.

I did 4 optimizations: two using bohr as input unit, two
angstrom, each one with symmetry turned on or off.

Observations:
1) All optimization seem to make unreasonable displacements
after the first optimization step (with gradients being
fairly small).
2) The problem is much more severe when using bohr as input
unit.
3) Turning off symmetry yields slightly different gradients
in the "bohr" case (by about 10^-7 au), which has fairly
significant influence on the displaced geometry after
optimization cycle 1. This is not seen for the "angstrom"
case.
4) There appears to be an "optimization cycle 0" (at least
I see the sequence SCF -> gradient -> displacement -> SCF ->
gradient -> Output on "optimization cycle 1 -> displacement ->...
For cycle 0, things still seem to be alright.
5) The full point group D2d is recognized only in the "bohr case",
only Cs is recognized in the "Angstrom case". In either case,
only C1 is found after the first displacement.

Note that the displacements for the "bohr case" are really
outrageous, essentially dissociating the molecule. But also
in the "Angstrom case" they are large enough to increase
the energy by about 20 mEh and let the optimization proceed
oscillatorily.

I did the same calculation with Gaussian, which converges
in 4 optimization cycles, lowering the energy by about 1.1 mEh.
Initial energy and gradient norm are both reproduced to better than
10^-7 au by MRCC.

I ran another molecule (benzene), for which I did not spot any
problems.

Any help is greatly appreciated....

Best regards,
Dirk Bakowies
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1 week 6 days ago #972 by jcsontos
Hi,
could you attach the inputs and outputs?
Best,
Jozsef

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1 week 6 days ago #974 by bakowies
Dear Jozsef,

I tried, but somehow it didn't seem to work ....
Trying again...

Dirk

File Attachment:

File Name: mrcc_geo_a...7.tar.gz
File Size:108 KB
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3 days 16 hours ago #984 by jcsontos
Hi Dirk,

thanks for the report, I've been still working on the fix.
It's really a peculiar one, has something to do with compiler code optimization as well.

Best,
Jozsef

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3 days 12 hours ago #986 by bakowies
Jozsef,
thanks for the update. And good luck with fixing the issue.
Best,
Dirk

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