0 votes
asked by (340 points)

Hi Miles,

I'm trying to calculate observables from idmrg. The scheme used in the sample "idmrg.cc" is base on the right-orthogonal gauge. But when I use the following code to check the orthogonality, it turns that this condition is not satisfied in the middle of the unicell

int Nuc = 4;
int N = 2*Nuc;
// Other codes
 for(auto ni=1;ni<=N;++ni)
{
    auto pa=psi.A(ni);
    auto indc = commonIndex(pa,psi.A(ni-1));
    PrintDat(pa*prime(dag(pa),indc));
}

where right-orthogonality is satisfied except for the center tensor, i.e., ni=5. The result for that site is not an identity matrix.

Best,
Su Wei

1 Answer

0 votes
answered by (34k points)

Hi, sorry for the very slow reply. I think the issue may be where you write

psi.A(ni-1)

The .A method of an MPS is 1-indexed. On the other hand, it does allow you to input A(0), but this retrieves the "center" tensor which has no site index, and is the singular values resulting from a Schmidt decomposition of the infinite system done between two unit cells. So it should not obey the right-orthogonal gauge. I understand this is not well documented. So for version 3 we are moving the iDMRG code to a separate "code" project and planning to replace it with a better implementation that is also better documented.

Best regards,
Miles

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