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Messages - mctdhb

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1
Hi there,

It's of importance for what specific problem you ask this question.

For contact interactions, we usually directly evaluate the W_sl integrals analytically and work with this.
There's thus no difference with the analytical delta distribution. In more than one spatial dimension, however, issues do arise with contact potentials.

Then, in >1D, one needs either renormalization or just to consider a short-ranged interaction with the same scattering properties (see for instance: Phys. Rev. A 87, 033631 (2013) ).

Regards,
Axel

2
Analysis Program Usage / Re: Memory errors when Phase, Gradient = .T.
« on: December 27, 2017, 08:58:53 PM »
Hi there,

Sorry for the late reply. Can you please provide the analysis.inp file which you have used and tell us what kind of computation you are trying to analyze?

The error looks like a problem with the FFTs. If I remember correctly, we only implemented the Phase analysis for two-dimensional problems. Did you try to run it on a one-dimensional computation?

Regards,
Axel

P.S.: If you need a faster answer, please send email to mctdhx@ultracold.org in the future.


3
Main Program Usage / Re: Estimation of Memory in Relaxation.
« on: December 04, 2017, 09:18:03 AM »
Hi there!

The memory needed for a computation with MCTDH-B for the coefficients is (N+M-1 over N)*(16 bytes [double precision complex])*(Dimension of Krylov subspace used for the integrator). The size of the Krylov subspace is adaptive, i.e., it depends on the particular problem studied; but it can be controlled using the "Minimal_Krylov" and "Maximal_Krylov" inputs in the MCTDHX.inp file.

In addition, M*N_g*[O(10)]*(16 bytes [double precision complex]) of memory is needed for the solution of the orbital equation.

Regards,
Axel

4
General Questions and Discussion / MCTDH-X Synopsis
« on: May 09, 2017, 11:49:36 AM »
What MCTDH-X is and what it can do

MCTDH-X is a unique method that -- roughly speaking -- allows one to describe the way little particles behave according to quantum physics. The MCTDH-X software is an implementation of that theory that allows to compute and visualize these quantum dynamics. Specifically, it is a way compute some fundamental properties of ensembles of indistinguishable particles, that is gases of atoms, that are constrained in a box or container at extremely low temperatures or electrons in atoms or molecules.

These properties can be collective, i.e., followed by all (or almost all) particles of the system or not. In the former case one is talking about a Bose-Einstein condensate if the considered particles are indistinguishable bosons or uncorrelated fermions if the considered particles are indistinguishable fermions; in the latter case, the we speak about something more complicated, a so-called fragmented many-boson or a correlated many-fermion state. Indistinguishable bosons at low temperature or indistinguishable electrons in atoms or molecules behave quantum-mechanically: they are wave-like in nature and, hence, totally different than ordinary matter. In a Bose-Einstein condensate (BEC), for instance, all the indistinguishable particles of the gas behave as if they were single effective particle.

Quantum fluctuations and correlations are negligible -- such a behavior is referred to as coherent for bosons and single-configurational for fermions. However, there are many cases in which this not true, even at ultracold temperatures. Phenomena like fragmentation and  correlations become very important. In such cases MCTDH-X is applicable, but conventional mean-field descriptions fail. MCTDH-X is designed to solve many-body dynamics of small and intermediate systems of ultracold particles (bosons or fermions) and shed light at phenomena where correlations emerge and mean-field approaches break down.     

The fundamental physical equation that governs the evolution of atomic and quantum systems is the Schrödinger equation. MCTDH-X is a method that can, in principle, describe these quantum dynamics exactly, i.e., to any desired given numerical accuracy, for a wide range of scenarios. To see more details about the MCTDH-X method and software, just click here:  http://ultracold.org/menu/


5
Analysis Program Usage / R-MCTDHB Synopsis
« on: October 17, 2013, 11:50:07 PM »
The Recursive implementation of the multiconfigurational time-dependent Hartree for bosons

What is it?
A collection of programs and scripts to solve exactly the time-dependent many-boson Schr?dinger equation and visualize the obtained solutions. The numerical solution of the problem is obtained with an efficient, shared and distributed memory-parallelized Fortran program that can be used with bash scripts or through a graphical user interface. From the simulation's output, graphs and videos are generated by invoking bash scripts that use mencoder and gnuplot for the task.

How it is documented?
The usage of the program is documented in a user manual and the code is documented in doxygen-generated html pages containing call- and caller-graphs.

How is it managed?
The code is version managed by mercurial (hg).

What does it need?
The program package can be installed on any Linux/Unix-based system that has a bash-shell, GCC or Intel Fortran compilers, and LAPACK, FFTW, and/or Intel MKL.

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