HF failing when using larger basis sets using the X2C Hamiltonian

[Ruairi Graham]

Hi,

I am trying to run some HF calculations on BaH using the X2C Hamiltonian. This works fine up to dyall.v4z but then when i try and augment Ba I begin to see problems. The calculation seems to fail when I use only the X2C Hamiltonian and so I then had to add the XAMFI keyword to the input which did help calculations converge at longer bond lengths, however, at short bond lengths I either just get NaN or a very large negative number. I cannot seem to explain why this happens at shorter bond lengths. Any advice would be greatly appreciated.

Kind Regards,

Ruairi 

[Miroslav Iliaš]

Dear Ruairi,

please send your inputs/outputs so that we see what is going wrong.

Miro

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[Trond Saue]

Hi Ruairi,

can you send an output file showing the problem ?

Best regards,

   Trond

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Trond Saue
Laboratoire de Chimie et Physique Quantiques
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[Ruairi Graham]

Hi,

I have attached the output file for a short bond length in BaH which has a very unusual HF energy (around -80,000 hartrees). 

Kind Regards,

Ruairi

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[Kenneth Dyall]

You might be running into linear dependence problems. What's the smallest eigenvalue of the overlap matrix?

Ken.

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[Hans Jørgen Aagaard Jensen]

Hi,

You have found a bug in the X2c transformation, probably caused by the linear dependency among the basis functions (maybe the X2c transformation has never been tried before with basis sets with linear dependency ...).

It becomes clear when you look at the orbital energies. The energy of the first occupied MO is close to -2mc^2, that is, it is a negative energy orbital ☹️

It will be fixed at the latest for the next release.

Best regards, Hans Jørgen.

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