Understanding the Differences Between Ising and Heisenberg Models

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Discussion Overview

The discussion focuses on the differences between the Ising model and the Heisenberg model in the context of statistical mechanics and spin systems. Participants explore theoretical aspects, potential simulations, and the implications of each model's structure and interactions.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested

Main Points Raised

  • Some participants note that the Ising model restricts spins to -1 or 1 in a given direction, while the Heisenberg model allows spins to point in any direction.
  • One participant questions whether the Heisenberg model can be simulated using Monte Carlo methods.
  • Another participant claims that both models allow only two spin states per lattice position, but highlights that the Ising model restricts interactions to nearest neighbors, which may not apply to the Heisenberg model.
  • One participant argues that the Ising model is semi-classical, treating spins as scalars, while the Heisenberg model employs quantum mechanical spin operators.
  • It is suggested that in the Ising model, only the z-components of the spin interact, whereas the Heisenberg model allows for interaction of all spin components.
  • A participant points out that the order parameter for the Ising model is one-dimensional (scalar), while for the Heisenberg model it is three-dimensional (vector), indicating different critical behaviors.
  • Another participant mentions that there are classical and quantum versions of the Ising model, suggesting a complexity in its classification.
  • One participant discusses the extension of both models over various lattice sites with differing couplings and describes the relationship between the Ising model and the Heisenberg model, noting that the Ising model can be viewed as a limit of the Heisenberg model under certain conditions.

Areas of Agreement / Disagreement

Participants express differing views on the nature of the models, their interactions, and their applications. There is no consensus on several points, particularly regarding the specifics of interactions and the implications of the models.

Contextual Notes

Some claims about the models' interactions and properties depend on specific definitions and assumptions that are not fully explored in the discussion.

rafizzi
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I've a problem to understand the Ising model and the Heisenberg model.
Can anyone explain to me what is the different between ising model and the Heisenberg model?
 
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In the Ising model the spins are allowed to be only -1 or 1 and in a given direction. In the Heisenberg model the spins are allowed to point in any direction.
 
can anyone explain briefly about the Heisenberg model and is it possible to simulate it with monte carlo simulation?
 
Hi,

I'm having the same doubt here.

I think that both models share in common that only two spin states are allowed for each position in the lattice. But while in the Ising model only nearest neighbours interactions are allowed, in the Heisenberg model this restriction does not apply.


Could anyone confirm this please.
 
No that's incorrect. The Ising model is semi-classical and treats spin in only parallel or antiparallel to a given direction (defined by the external field if included), and thus the spin is represented as a scalar. The Heisenberg model uses the appropriate quantum mechanical spin operators.
 
Alternatively you can say that in the Ising model, only the z-components of the spin interact while in the Heisenberg model, there is equal interaction of all components of spin.
 
The order parameter of Ising model is 1 dimensional, i.e. scalar, but that of Heisenberg model is 3, i.e. vector. So the critical behavior (scaling law) of these two models are different. They have different scalings.
 
nnnm4 said:
The Ising model is semi-classical and treats spin in only parallel or antiparallel to a given direction (defined by the external field if included), and thus the spin is represented as a scalar.

That is not entirely correct. There are classical and quantum versions of the Ising model.

Mavi
 
Also, we can extend both models over whatever range of lattice sites we like with differing couplings for nearest-neighbour, next-nearest-neighbour, and so on...

As was already said, the Ising model is a good model for when only the z components of the spins interact. Unfortunately, there isn't much in nature that can be modeled very well by it. The most general form of the Heisenberg model includes anisotropic couplings in the spatial directions, usually called the XYZ model.

The Ising model can then be viewed as a limit of the Heisenberg model when the couplings in the x-y plane vanish. If we let the coupling in the z-direction vanish, then we have the XY model, which is really quite an interesting model.
 

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