April 2020 - Comp-phys-alps-users

Unequal-time Green function in SSE QMC
by 郭怀明 11 Apr '20

11 Apr '20

Dear all, It seems to me that the realization of SSE QMC in ALPS does not measure the unequal-time Green function. Is there any possibility to revise the source code to add such a meansurement? Sincerely, Huaiming Guo

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eigenvectors
by Negin Mohseni 08 Apr '20

08 Apr '20

Dear All, Firstly I thank Rongyang for his fruitful explanation and suggestions. He assured me that I had thought correctly. In fact, in our work I must have all eigenvectors of a system. For this reason, I read tutorials related to exact diagonalization (ED) from sparse diagonalization to full diagonalization. Unfortunately, none of them fulfills my need. In most of tutorials the energy eigenvalues are sorted in several subspaces and momentums categories. But, I just wish to have a data set containing eigenvectors ignoring the dependence of momentum or subspaces. For example, for Ising chain in a transverse field ("h"), I wish to have the system's eigenvectors (as a list) and corresponded eigenvalues for each "h". How can we able to have a system's eigenvectors and corresponded eigenvalues? All the best

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Error in QMC with worm agrithm
by 郭怀明 07 Apr '20

07 Apr '20

Dear all, While I try to perform simulation using QMC with worm agrithm, I met an error related to HDF5. The information is attached as a file. I wonder how to fix the problem. Thank you for the helps! Sincerely, Huaiming Guo

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eigenvector from DMRG
by Negin Mohseni 06 Apr '20

06 Apr '20

I wish good health for all developers and users these days. My question is about DMRG process, We know that in DMRG procedure, while the size of the system grows, just the most important eigenvectors are kept (in each iteration). I think the 'MAXSTATES' in the DMRG code of ALPS package illustrates the maximum number of states from diagonalizing the reduced density matrix. Since the number of such states is less than the number of our system's state then we have an error in estimating energy of the system. But a question has occupied my mind: Does it make sense to ask the code to give the ground state eigenvector? Because with keeping a few numbers of the system's eigenvectors, I think in the last iteration, the output eigenvector is not corresponded to the whole system from the size point of view. We can consider a chain with 30 spin-1/2 particles. The ground state eigenvector of the system must be 2^30 in length . But I think the eigenvector of the last iteration from DMRG code is very smaller than 2^30 in length. Is this statement true? If it is correct, then how we can have the ground state eigenvector from ALPS DMRG?

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