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How to calculate the first, second... to 15 excited state in Tensor

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asked by (430 points)

Hi ITensor developer,
Thanks for your reply. I want to calculate The first, second, third,..... (to fifteen exited state) in 1D Heisenberg chain.(my ITensor is version 2 ). Please help me (give some sample) , Thank you very much !
Best,
Sugar

1 Answer

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answered by (70.1k points)

Hi, to do this you can use the excited state DMRG feature of ITensor. We have put “code formulas” (example codes) on the website at the following links, for each version of ITensor:

Version 2:
http://itensor.org/docs.cgi?vers=cppv2&page=formulas/excited_dmrg

Version 3:
http://itensor.org/docs.cgi?page=formulas/excited_dmrg&vers=cppv3

Please take care when using this method to compute highly excited states (or really any excited states). It’s important to converge the ground state very well. Also use many sweeps when converging the excited states. For the size of the “Weight” parameter you have to experiment to see what works best for the system you are studying.

Best regards,
Miles

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