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2003: Book chapter by Karen Hallberg. 2004: Reviews of Modern Physics by Ulrich Schollwoeck (2818 current citations). 2006: Advances in Physics by Karen Hallberg. 2008: JCTN: by Gabriele De Chiara and co-workers. 2011: ARPC: by Garnet Chan and Sandeep Sharma (426 current citations). 2014: The European Physical Journal D by Sebastian Wouters and Dimitri Van ...


17

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 $0.1$ to $0.7$ in increments of $0.1$, how do I spot the region of the critical coupling constant? There has to be a signature of the critical point that is ...


15

There are a few recent atomic partial charge schemes that are useful. You mentioned the electrostatic fitting schemes. These seek to best match the electrostatic potential of the molecule / system, but wouldn't be ideal for your situation. They have problems fitting charges on "buried atoms" such as the metal center of your complex, because they have little ...


15

This is an important question, and I will do my best to answer it in a way that adds to the nice suggestions made in earlier answers. In short, the answer is yes, but only with the help of some other models and approaches. In this response, I will focus on the conventional (computational) approach to this question, using lattice models and Monte Carlo ...


14

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 Carlo). You could directly look at the magnetization, but a more reliable signature is the magnetic susceptibility, $\chi_m (K)$, which is strongly peaked around ...


13

I am wondering if there is any computational method to know the curie temperature of magnetic materials? Yes, there is!. Simulations to determine Curie Temperature are usually done via Monte-Carlo methods, with the assumptions taken from the Heisenberg model. I haven't done any Curie Temperature Simulations using DFT but it is possible as this answer on ...


12

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 completely known, and the difficulty is only that the exact application of these laws leads to equations much too complicated to be soluble. It therefore becomes ...


11

Not a very thorough answer, but it should get the ball rolling. Spontaneous magnetization or extrinsically magnetic TIs have been achieved through defect engineering in non-magnetic Topological Insulators. This is typically done via doping of 3d magentic atoms (e.g. $\ce{Fe}$, $\ce{Mn}$). A recent review (2019) published in Nature Reviews Physics on the ...


11

First of all, you need to be familiar with models for magnetic exchange. Two important examples are Heisenberg and Ising: https://en.wikipedia.org/wiki/Heisenberg_model_(quantum) https://en.wikipedia.org/wiki/Ising_model Depending on the system you are studying, you will be using one or another. Typically, for very anisotropic spins with a very well ...


11

Changing ALGO should make no difference in an ideal world. However, when you invoke spin polarization, you may find a different magnetic state from both algorithms. The best practice would be to ensure that you converge to the right solution. That being said, the NORMAL algo is normally more robust than Fast. This in general might be a bad sign for your ...


10

The question highlights the difficulty in calculating an ab initio value for $T_{1/2}$ for a molecule like $\textrm{Fe(Phen)}_2\textrm{(SCN)}_2$, and specifically the fact that a highly cited 2018 paper predicts values that are between 60K and 278K higher than the experimental value of 176.5K. The paper highlights a major danger of using DFT, and in using ...


10

The anions of the form $\ce{MnO_x^y-}$ are referred to as manganates (see Wikipedia). I'm not sure if there might be a "special" name for $\ce{MnO2^-}$ specifically (that's the species you have here) because I never encountered this anion in my lab times, but given that $\ce{MnO4^2-}$ are the "normal" manganates and $\ce{MnO4^-}$ the permanganates, I think ...


10

Magnetic order and topological order can exist simultaneously. In fact, what one may call the very first proposal of an instrinsic topological material was Haldane's model from 1988, which is an example of this. In this tight binding model, based on a hexagonal 2-dimensional lattice (think graphene), we have a next-nearest-neighbour complex hopping term ...


10

(I'll answer with crystalline solids in mind.) You could study the material's magnetic and non-magnetic phases and construct their Gibbs free energy (G) vs temperature (T) profiles. \begin{equation} G\: =\: H_{T=0}\: +\: H_{T>0}\: +\: \text{zero point energy}\: -\: T\cdot S, \tag{1} \end{equation} Where H is enthalpy, and S is entropy (any kind). Based on ...


10

Structural: You should investigate the stability of your structure. In detail, you should verify: Dynamical stability: phonon spectrum. Thermal stability: molecular dynamics (MD) simulations Mechanical stability: elastic constants $\Rightarrow$ Born criteria Electronic: Band structure and density of states calculations. Maybe you should compare the ...


9

Unfortunately, without performing spin polarized calculations you cannot know if it will matter. Further, you must perform different magnetic configurations (AFM, FM, PM) to know which is stable. If you can experimentally show if its magnetic or not this will help. Certain elements tend to be magnetic as well. If you have Ni, Co, or Fe then you ...


9

It is an example where representative of different fields would give you very different answers. I do not want to pretend my answer would be by anyway complete. Short answer: yes. And the devil, as always, is in the details. Since we can solve Schrodinger and Dirac equations arbitrary accuracy (see eg Nakatsuji's work, http://qcri.or.jp/~nakatsuji/nakatsuji....


9

QuSpin QuSpin is an open-source Python code that can do exact diagonalization of spin, fermion, and boson systems. It has a wide support for use of symmetries, constrained Hilbert spaces, various models, and time evolution. The combination of fairly simple Python syntax and a large number of tutorials make it a great choice for beginners, for small-scale ...


9

You want the following flags in your INCAR to specify HSEsol: GGA = PS LHFCALC = .TRUE. HFSCREEN = 0.2 I also recommend setting Algo = All for smoother SCF convergence. The VASP manual suggests setting LASPH=.TRUE. as well for hybrid calculations, but that's a decision for you to make. In the future, if you are ever curious about how to define a given ...


8

At least in the example you picked up to illustrate your question, the key to the answer might be here: "The a axis, perpendicular to the chains in the structure, is the magnetic easy axis, while the chain axis direction, along b, is the hard axis." This means that the effectively infinite magnetic moments corresponding to each infinite one-dimensional ...


8

I agree with Tristan that the fool proof method is to do a spin-polarized self consistent calculation and look at the final magnetic moment. If the final magnetic moment is non-zero you should include spin polarization in your calculations. However, from a practical point of view you can have a look at the existing databases. In particular if you are working ...


8

This took some digging, but I can supply at least a partial answer. Assuming you can copy the list of magnetic moments to a list, you could trick whatever software you are using for visualization into outputting it indirectly. A typical POSCAR can look like the following. H 1.00000000000000 25 0 0 0 25 0 0 0 25 H 2 Selective dynamics ...


8

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 magnetization \begin{equation} m = \frac{\sum_i s_i}{N} \end{equation} has a symmetry that $\mathrm{Prob}[m=+m_0]=\mathrm{Prob}[m=-m_0]$, since the energy of a particular ...


8

Looking at your input and output files, I think the most likely explanation is a different local minimum in the energy, as mentioned by Andrew in the comments. If you look at the final scf step in the vc-relax output, it uses the starting magnetization from the last bfgs step, not the initial values you used at the start of the vc-relax. I would try two ...


8

Edit: This no longer seems to be the issue, as the atomic positions are apparently essentially unchanged, per @KevinJ.M.'s comment. I will nonetheless keep the answer here because it is still important to consider going forward. It looks like you are getting a different magnetization because the structures are not identical. Your first structure is fully ...


7

Topological magnon band structures Another way of combining topology and magnetism is to consider a magnetic insulator with non-trivial magnon band structure. This setting is somewhat different from the usual picture of topological electron band structure in that i) the band structure represents only quasiparticle excitations, ii) the quasiparticles are ...


7

1D A famous example of a nearly ideal spin-$1/2$ isotropic Heisenberg antiferromagnetic chain (1D) system is copper pyrazine dinitrate [Cu(C$_4$H$_4$N$_2$)(NO$_3$)$_2$], which was discussed in Hammar et al. Phys. Rev. B 59, 1008 (1999) [arXiv link]. Another excellent realizations include KCuF$_3$, which has stronger (but still low) interchain coupling, and ...


7

With the Materials Project and magnetism, it's often useful to download the structure directly and examine the magnetic moments on that structure, for example using the pymatgen Python code and the MPRester class, like so: from pymatgen import MPRester with MPRester() as mpr: # you may need to supply your API key in the parentheses here, see ...


6

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 experiment and easy to extract from numerics (or with a well-established theoretical value). In practice, the choice of which quantity to use will depend on ...


6

First, I would recommend reading through the pw.scf input file description, provided here. The relevant parameters are in the &SYSTEM namelist of the input file. To do a basic, linear spin-polarized calculation, you would need to set at least two additional parameters. If I have two types of atom, say, Fe and O, then if Fe is listed first under atomic ...


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