[ALPS-users] DMRG measurements of observables with support only on some lattice sites

[Axel Gagge]

Never mind, I solved the problem. I post the answer here just in case anyone else gets stuck on such a detail like me.


In the site basis, you simply define an operator with the same name but with some dummy value. For example, in the site basis of a boson:


<OPERATOR name="Sz" matrixelement="1"/>?


It is now safe to measure Sz on all sites (and discard the value on the bosonic sites).


If there is a way in ALPS to do this without a hack, I would be pleased to know!


/Axel



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Från: Comp-phys-alps-users <comp-phys-alps-users-bounces at lists.phys.ethz.ch> för Axel Gagge <axel.gagge at fysik.su.se>
Skickat: den 9 maj 2017 17:58
Till: comp-phys-alps-users
Ämne: [ALPS-users] DMRG measurements of observables with support only on some lattice sites


Hello all,


I am working with DMRG for a model where the unit cell consists of two lattice sites of different types (one is a boson mode while the other is a two-level/spin 1/2). Now, I want to measure say the expectation value <Sz> of my ground state on all the spin sites - how can I do this in ALPS? If I use MEASURE_LOCAL, ALPS tries to compute the expectation value of Sz for the boson sites and crashes.


MEASURE_LOCAL_AT seems like the reasonable thing to work with, but does it also work for expectation values?


Best regards,

Axel

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