Author Topic: Difference in the results between "type 2" and IMEST interaction for a 2D system  (Read 1658 times)

chrisapo

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Hi. I'm performing some trial simulation with MCTDH-X and I found some apparently inconsistent results.

I tried to simulate 2 bosons with 4 orbitals, trapped in a 2D parabolic well (whichpot="HO2D") and with a gaussian interaction.
I performed two relaxation simulations, the first one with Interaction_Type=2 (interaction dependent on the distance) and the second one with Interaction_Type=4 (IMEST).
Apart from the parameter Interaction_Type, the two MCTDHX.inp files were exactly the same in the two cases.

I expected to obtain the same results in the two cases, apart from rounding errors, but I didn't. The type 2 interaction gave me a ground state energy of around 2.73, while type 4 interaction gave around 3.11. I attached the two input files, so that you can try to reproduce the results.

This is in stark contrast with the results that I obtained in 1D, where type 2 and type 4 interactions gave always identical results (differences appeared only after several significant digits).

I'm struggling to understand the reason for this discrepancy. Is there something that I overlooked? Or maybe there is some bug related to dimensionality?

Any help would be greatly appreciated. Thank you in advance.

mctdhb

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Hi Chrisapo,

thanks for pointing out that there's an issue.

Please stick with
Code: [Select]
Interaction_Type=4, these results are correct and by
far the most efficient.

Interaction_Type=2 is intended for 1D computations only. Doing checks with the other settings (Interaction_Type=1 and 3), I found and rectified a bug with Interaction_Type=1 (the width was set to pi, irrespective of the user input).

The fix that should give the same result for Interaction_Type=1,3, and 4 is now in the repository, please get it via
Code: [Select]
hg pull.

Hope this helps,
Axel