Dear ALPS developers and users,
I am running a DMRG simulation with alps on a Heisenberg chain with
periodic boundary conditions. My parameter file is
'LATTICE' : "chain lattice",
'MODEL' : "spin",
'CONSERVED_QUANTUMNUMBERS' : 'Sz',
'L' : 24,
'Sz_total' : 0,
'Jxy' : 1,
'Jz' : 3,
'SWEEPS' : 4,
'NUM_WARMUP_STATES' : 100,
'MAXSTATES' : 100,
'NUMBER_EIGENVALUES' : 1,
'MEASURE_LOCAL[Local magnetization]' : 'Sz'
In this regime I know the ground state has null global magnetization. As I
am considering periodic boundaries, my results should be translationally
invariant, and I should get a null local magnetization as well.
Strangely enough though, when I check the local magnetization (last line of
parameter file), I get a non-zero value.
If I consider small L I find a local magnetization of the order E-7, which
means practically 0. But when I grow the chain, this number rises, and in
the case I am attaching is alternating, and of order 0.0275.
How could it be possible? Are not periodic boundary conditions enough to
constrain to impose invariance under translation in the final state?
Moreover it really looks like considering more states and sweeping more
doesn't help.
Thanks in advance for any help.
Kindest regards.
--
Emanuele Levi
emanuele.levi(a)gmail.com