0 votes
asked by (130 points)
edited by

Hi,
I am trying to time evolution of a wave-packet using MPO time evolution, with multi-Hubbard Hamiltonian, which has four operator terms.
ampo +=Jh,"Cdagdn",b,"Cdagup",b,"Cup",b+1,"Cdn",b+1;
ampo +=Jh,"Cdagdn",b+1,"Cdagup",b+1,"Cup",b,"Cdn",b;
Where, I found the problem with "auto expH = toExpH(ampo,tau*Cplx_i);;"
while running it's give error:

From line 1490, file mps/autompo.cc

Only at most 2-operator terms allowed for AutoMPO conversion to MPO/IQMPO

Only at most 2-operator terms allowed for AutoMPO conversion to MPO/IQMPO
Aborted (core dumped)

Please help me to solve this issue.

1 Answer

+1 vote
answered by (35.1k points)

Hi, so unfortunately our toExpH feature is limited to Hamiltonians consisting of at most 2-operator terms only. The reason is that it's technical to extend the same method that lets AutoMPO work for > 2 operator terms to also define the exponential of H, even though in principle this could be done perhaps.

But additionally, since implementing toExpH, we and the tensor network community have found that MPO-based time evolution is not a particulary reliable or accurate time-evolution method (in relative terms, since it does work but just not as well) compared to other methods. The best method to use would be TDVP which only needs the Hamiltonian MPO as input. (See the recent review by Paeckel et al. for a technical discussion of both time-evolution methods.) So this is unfortunate given the convenience of MPO methods, but is a useful thing to keep in mind.

Best regards,
Miles

Welcome to ITensor Support Q&A, where you can ask questions and receive answers from other members of the community.

Formatting Tips:
  • To format code, indent by four spaces
  • To format inline LaTeX, surround it by @@ on both sides
  • To format LaTeX on its own line, surround it by $$ above and below
  • For LaTeX, it may be necessary to backslash-escape underscore characters to obtain proper formatting. So for example writing \sum\_i to represent a sum over i.
If you cannot register due to firewall issues (e.g. you cannot see the capcha box) please email Miles Stoudenmire to ask for an account.

To report ITensor bugs, please use the issue tracker.

Categories

...