20 votes

What are good random number generators for Monte Carlo calculations?

Depending on how many random numbers you need in a short amount of time, it might be worth to consider using a cryptographic PRNG. In particular AES-CTR. Now of course you might say that "but AES-...
  • 301
17 votes
Accepted

Ising model: How can I spot the critical point?

My question is, when I run a simulation with $N$ particles and I track the Hamiltonian per particle $(H/N)$ and the magnetization per particle $\left(\sum _i s_i /N\right)$, with $K$ values going from ...
  • 4,238
14 votes

Ising model: How can I spot the critical point?

As Anyon correctly pointed out, there is no phase transition at finite temperature in 1D. In 2D there are a number of different ways to identify the phase transition (I'm assuming you're using Monte ...
14 votes

What are good random number generators for Monte Carlo calculations?

It's been years since I've done Monte Carlo calculations (though it was more recent than the 90's!), so hopefully the information given below is still reasonably up-to-date. I've also had reason to ...
  • 4,238
12 votes
Accepted

Is Heisenberg model or in its simplier form Ising model a good approximation to study magnetic systems?

Introduction Your question reminds me of a quote by Paul Dirac, The underlying physical laws necessary for the mathematical theory of a large part of physics and the whole of chemistry are thus ...
  • 4,238
10 votes
Accepted

Autocorrelation function problem in Monte Carlo simulation of 2D Ising model

First, some general remarks: The measurements should be made after the system has equilibrated, i.e., a large number of the first iterations should be discarded before the analysis. They should also ...
  • 786
8 votes

Autocorrelation function problem in Monte Carlo simulation of 2D Ising model

@stafusa's answer is great, but there is a specific phenomenon you are encountering here called critical slowing down, which is especially bad for the single-spin-flip Metropolis Algorithm. Near the ...
8 votes

Ising model: How can I spot the critical point?

I think Anyon's and taciteloquence's answers are perfect. I just want to add an emphasis on the following fact that frequently leads to confusion for beginners. The formal definition of the ...
7 votes
Accepted

What is the fundamental difference between the Ising and Potts models?

Fundamentally, there is not much of a difference. A Potts model is a kind of generalized Ising model that includes more spin states. The Hamiltonians can be written with similar forms. The Ising model ...
6 votes

What measured quantity can be associated to the value of the J parameter in the Heisenberg/Ising hamiltonians?

Here I'll assume that the material is already believed to be roughly described by a model of the Heisenberg or Ising form. In that case, you just want a quantity that is easy to measure in your ...
5 votes

Ising models with many-body interactions

As a (very) incomplete answer to this question, here is one paper discussing the Ising FM with a plaquette term. Here specifically chosen because there was not a good cluster algorithm for it (so they ...
4 votes

Is it possible to calculate/estimate the value of the J parameter to be used in the Heisenberg/Ising Hamiltonians?

The equation in your question, be it Heisenberg or Ising exchange, can be calculated by Energy mapping analysis. This has to be the most popular paper that discusses this technique. Basically, you ...
  • 2,212
4 votes

What is a "transient" state?

The excerpt that you gave us defines a steady state as one in which the state is not changing ($\frac{\textrm{d}\rho}{\textrm{d}t} = 0$) and a transient state in which the state is changing ($\frac{\...
  • 29.1k
3 votes

What's the most efficient way to obtain the ground state of spin models exactly?

No, the quantum version is not simpler There are many ways to find the ground state of an arbitrary quantum system. Quantum Monte Carlo (QMC), Density Matrix Renormalization Group (DMRG), et. al., but ...
3 votes

What is a "transient" state?

Transient state can be defined as a state in which $\frac{\text{d} \rho}{\text{dt}} \neq 0$, which, in an Ising Model MCMC (or any step-based) simulation, could be translated to $\frac{\text{d} M}{\...
2 votes

Is there any useful application to estimating the expectation value for an Ising model without magnetic field?

"I know that one "hot question" about the Ising model is to be able to find its ground state. However this ground state in the absence of magnetic field is necessarily a tensor product (...
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