Questions tagged [spin-models]

Questions related to spin models wrt materials modeling.

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6
votes
1answer
40 views

How to choose half-Brillouin-zone (HBZ) in Fukui & Hatsugai's numerical scheme for the Z2 invariant?

EDIT: Please see my first comment on this question first. In this paper, Fukui and Hatsugai present a numerical scheme for the calculation of the $\mathbb{Z}_2$ index that uses the following ...
7
votes
1answer
49 views

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

(Note: an earlier version of this question had been asked on Phys.SE before) It is known that finding the ground state of classical spin glasses is NP-hard: it will take (at least) an exponential ...
18
votes
3answers
641 views

Ising model: How can I spot the critical point?

Consider a zero-field Ising model with $N$ spins and periodic boundary conditions, with the Hamiltonian given by: $$H = -K \sum _{(ij)} s_i s_j\tag{1}$$ in 1D and 2D, where $K = \frac{J}{k_BT}$, where ...
6
votes
1answer
442 views

How to choose starting magnetization while doing spin polarised calculation in Quantum ESPRESSO?

I am trying to run spin polarised DFT calculation in Quantum ESPRESSO on system Co2MnSi. I kept starting magnetization for all these three species as, ...
7
votes
2answers
79 views

What packages exist for building quantum Monte Carlo simulations of spin or Hubbard Hamiltonians?

What packages exist that can help someone, especially a new masters/PhD student get started with QMC on spin or Hubbard systems? As an example, for writing a stochastic series expansion QMC program ...
11
votes
1answer
131 views

Ising models with many-body interactions

I find it surprisingly difficult to find researches/papers on systematic "many-body interaction" extensions of the Ising model. Can somebody tell me a good review/article etc on this matter ...
9
votes
0answers
66 views

How to choose the values of J and spin parameters in a heterogeneous spin system?

In this work, graphene-based systems that are described by mixed spin-3/2 and spin-5/2 are studied using the ising-model. A diagram of the structure is shown bellow: The Hamiltonian used is: \begin{...
18
votes
2answers
411 views

What are good random number generators for Monte Carlo calculations?

Many problems in Computational Physics need the use of random number generators. When studying magnetic materials using the Heisenberg/Ising Hamiltonians (related questions about them can be seen here,...
7
votes
1answer
96 views

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

This question is related to other one here in the MatterModelingSE: Is it possible to calculate/estimate the value of the J parameter to be used in the Heisenberg/Ising hamiltonians? Here J is the ...
6
votes
1answer
129 views

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

Studying magnetic systems, two frequently used approximations are the Heisenberg and Ising models (a discussion about these approximations can be read here): \begin{equation} \tag{Heisenberg} \hat{H}...
12
votes
2answers
188 views

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

Currently, I did a Monte Carlo simulation with the local update and Wolff cluster updated in 2D classical Ising model. I use the autocorrelation function to compare 2 different algorithm in critical ...
16
votes
2answers
70 views

Is there a list of models that do and do not have the QMC sign problem?

The sign problem is a huge limitation of QMC, but it's not easy to tell by looking at a Hamiltonian if it has the sign problem. Often there will be some clever transformation that allows you to avoid ...
24
votes
3answers
226 views

What are examples of materials that closely correspond to the Heisenberg model?

I use the antiferromagnetic Heisenberg model all the time: $ H = J \sum \limits_{\langle i,j \rangle} \vec S_i \cdot \vec S_j$ What are some examples of materials that are well-described by this ...