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Questions tagged [condensed-matter]

For all matters related to condensed matter physics.

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6
votes
1answer
34 views

What is signified by the properties of the electronic band structure?

When considering the band structure of two materials or two structures along a specific k path, what exactly is meant by the gradient and the distance between band lines? Does this show any ...
5
votes
0answers
53 views

DMRG packages with an easy learning curve for studying the quantum spin systems at zero as well as finite T

What are the DMRG packages with an easy learning curve for studying the quantum spin systems for following purpose: Finding the magnetization curves (M vs H) for 1D spin Hamiltonians [Heisenberg ...
5
votes
0answers
33 views

Constructing the symmetry operator from k.p Hamiltonian

I have a question regarding to how to construct an operator from k.p Hamiltonian. Maybe there are some problems in my understanding, I hope you can point me out and correct my description if I made ...
6
votes
1answer
48 views

Imaginary time dependent operators: (anti)commutation relations

If I know trivial (anti)commutation relation for some operators (let's say Fermi operators), I can only use it if they are in the same moment of time. If I have their time dependence and they don't ...
4
votes
1answer
54 views

Hubbard model SU(2) symmetry: manifest invariance

Could someone explain, is it possible to make Hubbard Hamiltonian manifestly SU(2) invariant? I know about the interaction term, but how would kinetic (hopping effect) term have to look like? Here I'm ...
6
votes
1answer
45 views

Confusions in interpreting Dirac strings (wormholes) in Haldane's Hilbert space picture ft. two tori joined by strings at gapless points

I had a question about Haldane's wormhole interpretation (picture below). I believe he first proposed it in his paper Berry Curvature on the Fermi Surface: Anomalous Hall Effect as a Topological Fermi-...
6
votes
1answer
64 views

Help with definitions in k-space twisted bilayer graphene model

I am trying to numerically do calculations using Eq. 8 of MacDonald's simple model for twisted Bilayer graphene. I only want to calculate the Berry phase. However, I don't think I have my definitions ...
5
votes
0answers
28 views

Example of 2D k-space models allowing interband transitions after a closed-loop trajectory?

I have been mainly exposed to 2D momentum-space condensed matter models in the context of Berry-related topology. I now want to study models where, if I take a closed loop in momentum space, I will ...
6
votes
2answers
210 views

POSCAR data file for a 2D system

I would like to understand how to calculate the band structure of the Graphene monolayer system using DFT. I am using VASP for material simulation. My question is how to write the crystal structure ...
7
votes
0answers
37 views

The quantum spin Hall phase with Z2 = 0?

I used first principle calculations to study the thin film model. An obvious crossing was shown to appear at the gamma point when the edge state was calculated, which was originally predicted to be ...
11
votes
1answer
153 views

How to use wavefunctions/density to determine which orbitals lead to edge states?

I have a large matrix for a 1D zigzag edge model of an otherwise $3\times 3$ tight-binding Hamiltonian (3 basis functions, each corresponding to an atomic orbital), involving the variable $k_x$. The ...
9
votes
1answer
209 views

Help with translating Hamiltonian into matrix

Eq. 19 in this paper gives the following Hamiltonian: $\sigma_a, \tau_a, \eta_a$ are respectively the spin, sublattice pseudospin and valley pseudospin respectively. Normally, I would have chosen a ...
4
votes
0answers
41 views

Z2 topological index: Is this unconventional formula summed over just filled bands, or all bands?

The $\mathbb{Z}_2$ topological index is usually defined in terms of the Pfaffian of the overlap matrix, as defined by eq. 4 of Kane and Mele's paper: $$ P(k)=\text{Pf}[\langle u_i(k) | \Theta | u_j(k) ...
7
votes
1answer
84 views

Help with Definitions in Numerical Calculation of Multiband Berry Phase

In the third chapter of Vanderbilt's book, they discuss the so-called multiband parallel transport and provide a scheme for numerical calculations that is similar to the single band case (where the ...
12
votes
1answer
123 views

How to numerically solve real-space 1D time-independent Schrodinger equation using 2D momentum-space Hamiltonian?

Consider the usual simple 2-level graphene Hamiltonian with mass in momentum-space where: $$ H(k,V)=-t \sum_{\delta} [\cos(k\cdot\delta)\sigma_x-\sin(k\cdot\delta)\sigma_y+V\sigma_z], $$ where $t$ is ...
5
votes
0answers
39 views

Help with understanding topologically-protected edge states in domain wall systems

Let's say that I have a simple domain wall system for the following Hamiltonian with added on-site potential $M(x)$: $$ H(k,M)=-t \sum_{\delta} [\cos(k\cdot\delta)\sigma_x-\sin(k\cdot\delta)\sigma_y+M(...
5
votes
0answers
60 views

Wavefunction magnitudes being degenerate everywhere on parameter space even though energy degeneracies occur at isolated points?

Cross-posted here: https://physics.stackexchange.com/questions/635887/wavefunction-magnitudes-being-degenerate-everywhere-on-parameter-space-even-thou Consider the usual simple 2-level gapless ...
8
votes
0answers
64 views

What are some types of topologically-relevant band degeneracies in contemporary 2D condensed matter research?

Cross-posted on Physics.SE. In the study of 2D condensed matter systems, I have seen several kinds of band degeneracies. I call 'bands' the eigenvalues to the time-independent Schrodinger equation, ...
16
votes
3answers
2k views

What does “strongly correlated” mean?

For quantum many body problem, there is a common terminology “strong correlated systems” that appears in different context. However, it seems that the definition of it is ambiguous and sometimes ...
10
votes
2answers
381 views

How can we say that the KS equation is describing a noninteracting many-electron system?

Based on HK's two theorems, the density functional theory was built. Because one can't find the universal energy functional $F_{HK}[n(r)]$, Kohn and Sham further proposed the Kohn-Sham ansatz: mapping ...
10
votes
1answer
100 views

How can I calculate the J value in an antiferromagnetic material?

I am new to DFT, especially in doing DFT for magnetic materials. I recently came across this paper which indicated the calculation of the J value in the case of antiferromagentic materials as per the ...
6
votes
0answers
73 views

Example of a standard/archetypal/simple 4-band gapped condensed matter model with analytic results?

I am looking to study Berry phase-like phenomena in a gapped 4-band material model. In particular, I want to numerically and analytically calculate the Abelian Berry curvature integral of each band ...
6
votes
1answer
58 views

Example of a standard/archetypal/simple 4-band un-gapped condensed matter model with analytic results?

I am looking to study Berry phase-like phenomena in an un-gapped material model. However, I am having trouble finding a widely-used 4-band model with analytic expressions for wavefunctions and ...
10
votes
1answer
286 views

What's the past and future of 2D materials since graphene?

Since the discovery of graphene in 2004, two-dimensional (2D) materials have been a hot topic in the community of condensed matter physics, which can be considered as the candidate for next-generation ...
5
votes
0answers
71 views

Why does numerical computation of Berry curvature give me a correct Berry phase when it is supposed to diverge?

I implemented the standard numerical algorithm for calculating the Berry curvature in MATLAB. For a given 2D system, I can visualize the Berry curvature over parameter space. If I sum the Berry ...
5
votes
1answer
60 views

Thermo-calc: Calculate precipitation driving force by parallel tangent construction

I want to calculate the difference in Gibbs free energies between a Zr-Cu-Al liquid (composition - Zr 65 Cu 27.5 Al 7.5 at%) and the CuZr2 solid phase as a function of temperature (300 - 1000 K). In ...
7
votes
0answers
89 views

How to fix gauge in Quantum ESPRESSO?

I am trying to use Quantum ESPRESSO to manually calculate the Berry phase using the Berry connection, due to evolution along a closed loop in k-space. I want to do this manually instead of using ...
6
votes
0answers
54 views

Value of density of state effective mass and transport effective mass to calculate conductivity [closed]

How can density of state effective mass and transport effective mass can be defined to calculate conductivity for a cubic system with parabolic but anisotropic dispersion relation? What will be the ...
12
votes
1answer
558 views

When do we abandon ab initio methods?

This question is related to (and was originally asked in) another post about "quantum protectorates" I made here. Ab initio methods are nice because they directly solve a sort of "...
5
votes
0answers
31 views

What's the difference between dynamic and static strain aging?

I do understand how static strain aging occurs and why the yield point comes back if ample time is allotted after a loading and unloading cycles primarily due to diffusion of substitutional and ...
5
votes
0answers
44 views

A doubt about extended dislocation [closed]

I wonder why this phenomenon occurs: "Unlike unextended screw dislocations, the extended screw dislocations define a specific slip plane, the {111} plane of the fault and it will be constrained ...
14
votes
1answer
111 views

What are the physical consequences of adding a constant to the diagonal of the effective Hamiltonian of monolayer materials?

Effective Hamiltonians modeling many-layered materials are often tuned using some sort of bias voltage. For instance, in a $4\times 4$ Hamiltonian matrix to describe biased bilayer graphene using some ...
3
votes
0answers
38 views

Doubt in Raoultian and Henrian Standard State [closed]

$Si(liq)=Si_\text{(1 wt% Fe)}$ Can you describe what is going on here?All that they ask for is change in Gibbs free energy for the process.I am completely unable to figure why this particular model is ...
6
votes
1answer
67 views

Where is this extra plane coming from?

Why are there solid lines drawn connecting the solid circles after twinning has taken place? Ideally, that explains a real plane, isn't it? But why are we going to get a plane out of nothing if we ...
13
votes
1answer
301 views

Software for solving quantum spin Hamiltonians in 1D and 2D

I'm looking to solve quantum spin Hamiltonians in 1D and 2D (e.g. Heisenberg Model) consisting of a large number of spin sites. What are the pros and cons of each package, and which package is more ...
10
votes
0answers
93 views

First principles calculations beyond s-wave BCS superconductors

Conventional superconductors are often modelled using Bardeen-Cooper-Schrieffer (BCS) theory with an s-wave order parameter, but not all superconductors describable with BCS theory have an s-wave ...
8
votes
1answer
66 views

How to predict new Half Metallic materials with higher degree of spin polarization?

Using DFT calculations, how one can predict the new half metallic materials with higher degree of spin polarization. I want to know the steps which have to be followed in prediction of new materials. ...
9
votes
2answers
659 views

How to choose pseudopotential for DFT calculations in Quantum ESPRESSO?

I am a beginner and newly started running DFT calculations to find out the electronic band structure of certain materials in Quantum ESPRESSO. But we have to select the pseudopotential for running the ...
12
votes
3answers
561 views

External magnetic field in VASP?

I have never found any tags or documentation regarding external magnetic field in VASP but in different well known published articles$^1$, the implementation of the external magnetic field by VASP has ...
8
votes
1answer
389 views

How to perform virtual crystal approximation calculations in VASP?

Can someone share appropriate tags and methods to perform virtual crystal approximation calculations in VASP?
11
votes
1answer
227 views

How to start with structural defects in monolayer?

First of all, thank you for your help! You are so helpful every time. I would like to calculate the influence of the structural defects on the electronic structure in the HfS2 monolayer. With VESTA ...
3
votes
1answer
61 views

How to simulate a furnace computationally

I am trying to synthesize MoSe$_2$ crystals in a furnace with two temperature zones. The problem is that the oven is not very wide, so the temperature of the hottest zone influences the temperature of ...
8
votes
0answers
46 views

Symmetry of glide planes [closed]

I am trying to understand the symmetry elements of space group number 194 (P$6_3$/mmc), which is hexagonal and has 24 symmetry operations. In the table of symmetry operations it says that it has three ...
8
votes
0answers
56 views

Structural biology vs condensed matter prediction

I have two main modeling research lines: one related to structural biology (including rational drug design, de novo design, polymorphism, etc.) and the other one related to condensed matter (...
12
votes
2answers
98 views

What are real examples where fractals were used in Matter Modeling?

A fractal is, accordingly Oxford English Dictionary: A curve or geometric figure, each part of which has the same statistical character as the whole. Fractals are useful in modeling structures (such ...
13
votes
1answer
153 views

Can we "invert" Density Functional Theory through sufficiently accurate experiment?

The famous Hohenberg-Kohn theorems say that there is a one-to-one mapping between the many-body Hamiltonian, $\mathcal{H}$, of a solid and its ground-state electron density $\rho(\mathbf{r})$. As far ...
15
votes
3answers
353 views

What are some codes available for Dynamical Mean Field Theory (DMFT)?

One particularly field of matter modeling is that of strongly correlated materials, heavy-fermion compounds with partially filled 4f or 5f orbitals. In brief, these are materials whose complex ...
5
votes
1answer
61 views

Property related with Berry curvature: $\Omega_{n,\mu\nu}=-\Omega_{n,\nu\mu}$

I read in David Vanderbilt's book named "Berry Phases in Electronic Structure Theory - Electric Polarization, Orbital Magnetization and Topological Insulators" the definition of Berry ...
16
votes
1answer
2k views

How to understand the time-reversal symmetry in graphene?

A lot of references say that the Dirac cone in graphene is protected by inversion and time-reversal symmetries. How can one understand this statement? How can one show explicitly that the gapless ...
11
votes
1answer
319 views

Real space projection vs reciprocal space projection in DFT calculations

When doing VASP calculations for large cells, we get a warning: "You have a (more or less) 'large supercell' and for larger cells it might be more efficient to use real space projection ...