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# Problem with geometry optimization

1 week 6 days ago #971
by bakowies

*Problem with geometry optimization*was created 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

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

Replied by

*jcsontos*on topic*Problem with geometry optimization*
Hi,

could you attach the inputs and outputs?

Best,

Jozsef

could you attach the inputs and outputs?

Best,

Jozsef

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1 week 6 days ago #974
by bakowies

Replied by

*bakowies*on topic*Problem with geometry optimization*
Dear Jozsef,

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

Trying again...

Dirk

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

Trying again...

Dirk

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3 days 16 hours ago #984
by jcsontos

Replied by

*jcsontos*on topic*Problem with geometry optimization*
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

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

Replied by

*bakowies*on topic*Problem with geometry optimization*
Jozsef,

thanks for the update. And good luck with fixing the issue.

Best,

Dirk

thanks for the update. And good luck with fixing the issue.

Best,

Dirk

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