Messages

1

Main Program Usage / Default choice of the starting orbitals

« on: February 10, 2020, 10:20:14 AM »

Hello. Thank you for your useful answers. I came up with a few others

I noticed that the default behavior of MCTDH-X's last version, when the GUESS='HAND' option is set, is to start from orbitals that are random functions. Is there a particular reason for this? Does the program work better with this random starting point?

Also, from this I deduce that the starting orbitals do not need to be orthogonal to each other. Am I correct?

2

Main Program Usage / What's the optimal number of threads in parallel computations?

« on: January 30, 2020, 11:58:43 PM »

Hello.
Regarding hybridly parallel computations, here's an excerpt from MCTDH-X's manual:

the most efficient way is usually to run MCTDH-X with at least as many MPI processes as there are orbitals. The OpenMP shared memory parallelization takes care of efficiently performing the computational task inside of each MPI process."

So, it is suggested a rule of thumb for the number of MPI processes: at least as many as there are orbitals. My question is then: is there a similar rule of thumb for the appropriate number of OpenMP threads (per MPI process)?

3

Main Program Usage / Is it possible to implement PBC?

« on: January 20, 2020, 01:31:45 PM »

Like the subject says, is there a way to implement Periodic Boundary Conditions, at least in 1D? Or is it a feature yet to come?
Just wondering.

4

Main Program Usage / Difference in the results between "type 2" and IMEST interaction for a 2D system

« on: January 20, 2020, 11:55:49 AM »

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.