ground state of a kondo problem with DMRG

DMRG and Numerical Methods
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Hi Miles,

Many thanks for the fast and detailed reply, and it works!

  1. I added eigsolve_krylovdim=10 to both the homogeneous and impurity cases. The DMRG gs energy for the impurity case got closer to ED. The gs expectation values were still pretty different from ED values for both cases.

  2. Then I added f electron hopping term t'=0.01. Still similar results for both cases: DMRG is not stopped early by the observer, and gs expectation values not good.

  3. I changed to t'=0.1. This time the first DMRG for system with t' got stopped by the observer after 10 sweeps. The second DMRG with t'=0 also converged after 6 sweeps. And the gs energy and expectation values were all close to ED, for both cases.

So my problem is solved and I really appreciate it. I don’t want to bother you more, but I get curious about what you mentioned:

and have several questions:

  1. It seems that I need to “connect” or “mix” the unit cells (A: c electron + B: f electron) by giving a not-too-small t'. And if I have (A: spin-1/2 + B: spin-1) unit cell like DMRG-Calculation-with-Mixed-Local-Hilbert-Space-Types or (A: spin + B: electron) unit cell like mixed-site-set-with-quantum-number-conservation, should I start with a system where A- and B-type sites are connected and then use the output MPS as input for the actual system?

  2. I am not familiar with the 3-site DMRG. Does the 3-site mean that for each dmrg sweep, 3 site tensors are updated at a time? I guess the 3-site DMRG can be good if I have 3 sites in the unit cell, like (A: c electron + B: f electron + C: d electron). It seems that the codes in the example/dmrg folder are all 2-site dmrg. How can I initialize a 3-site calculation?

Thanks again for your help!

Best,
Zhen