Hi Alex,

As usual, we can only help if you send both your input files and the results.

Best regards

Matthias

On May 14, 2015, at 22:01, Alexander Herzog Metalhead@web.de wrote:

Hello everybody,

the following might be stupid question or a question, which has already been adressed somewhere:

Does DMRG (or also ED for that matter) conserve equivalence between lattices and models?

Let me explain this question on the occasion of an example: I have created a lattice and a model for the 1D dimerized J1-J2-model, that is:

H=\sum_j^{L/2} (J_1(1-(-1)^j\delta)S_j*S_{j+1}+J_2\S_j*S_{j+2}).

In order to validate the lattice and the model, i ran the program for \delta=J_2=0 and J_1=1 for various lengths. In doing so, the ground state energy did not converge to e0=-0.443... but to a value close to it (something between -0.41 and -0.43 depending on the number of sweeps, warm-up states, states to be kept and on L). First I attributed this fact to finite size effects for one and numerical effects on the other hand. However to be sure I compared the model with the standard alps model for spin (with L sites, as in the case of the dimerized J1-J2 chain the unit-cell is doubled), which is the Heisenberg AFM chain and the outcome is different from the other result.

So now, I am asking myself, and I would like to raise the question within the ALPS community, whether this is plausible, as the numerics behind the scenes does not treat the two cases on equal footing, or whether I should critically reconsider the implementation of the dimierized J1-J2 model.

Thank you in advance,

Alex