Dear ALPS developers,
I was wondering about the meaning of the parameter SPINFLIP for the CT-HYB impurity solver. The documentation mentions:
SPINFLIP={0,1} specifies whether to perform spin flip updates. In such an update a segment is moved from one orbital to another, if the latter is empty.
Does this correspond to a global move that flips all spins, i.e. for enforcing a paramagnetic solution or does it correspond to the part of the rotationally invariant Hund's coupling which is called Spin-Flip term?
If it's the first one, are there any plans that Spin-Flip/Pair-Hopping terms can be treated within the CT-HYB solver in the near future?
best regards, Steffen
hi Steffen,
there are two relevant parameters:
SPINFLIP which does it only for one segment, and GLOBALFLIP which does it for all of them
Does this correspond to a global move that flips all spins, i.e. for enforcing a paramagnetic solution or does it correspond to the part of the rotationally invariant Hund's coupling which is called Spin-Flip term?
We do not have rotationally invariant Hunds coupling in this, so it’s the first: it takes segments from one orbital and moves the to another one.
Best, Emanuel
Hi Emanuel,
thanks for the explanation! What is your opinion about this? Is it safe to use or does it actually might "hide" problems with non-ergodicity? For example at higher interaction parameters for small Solver-times the up and down components are different, and such move might maybe lead to the wrong conclusion that the solver time is sufficient. Can one safely determine when this is the case?
bests, Steffen
hi Steffen,
there are two relevant parameters:
SPINFLIP which does it only for one segment, and GLOBALFLIP which does it for all of them
Does this correspond to a global move that flips all spins, i.e. for enforcing a paramagnetic solution or does it correspond to the part of the rotationally invariant Hund's coupling which is called Spin-Flip term?
We do not have rotationally invariant Hunds coupling in this, so it’s the first: it takes segments from one orbital and moves the to another one.
Best, Emanuel
Hi Steffen,
What is your opinion about this? Is it safe to use or does it actually might "hide" problems with non-ergodicity?
it’s an additional set of updates. It cannot make the system less ergodic: rather, it allows you to explore different parts of phase space and will make the system more ergodic.
For example at higher interaction parameters for small Solver-times the up and down components are different, and such move might maybe lead to the wrong conclusion that the solver time is sufficient. Can one safely determine when this is the case?
This is always a difficult problem. If you suspect ergodicity issues, have a look at your observables starting from high T (where the simulation should be ergodic) and examine the autocorrelation times. If you make a plot of the autocorrelation times vs T you should be able to detect if there’s a point where they diverge (and you stop being ergodic). If that’s the case, you’ll need additional updates.
The autocorrelation times are automatically measured in ALPS as ‘tau’ in your observables, but you’ll need to program their output manually.
Emanuel
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