Questions tagged [condensed-matter]
For all matters related to condensed matter physics.
54
questions
6
votes
2answers
141 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 ...
6
votes
0answers
22 views
The quantum spin 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 ...
10
votes
1answer
122 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
198 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
31 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:
$$
P(k)=\text{Pf}[\langle u_i(k) | \Theta | u_j(k) ...
7
votes
1answer
74 views
Help with Definitions in Numerical Calculation of Multiband Berry Phase
In the third chapter of Vanderbilt's book, they discuss the so-called multiband parallel transport and provide a scheme for numerical calculations that is similar to the single band case (where the ...
12
votes
1answer
102 views
How to numerically solve real-space 1D time-independent Schrodinger equation using 2D momentum-space Hamiltonian?
Consider the usual simple 2-level graphene Hamiltonian with mass in momentum-space where:
$$
H(k,V)=-t \sum_{\delta} [\cos(k\cdot\delta)\sigma_x-\sin(k\cdot\delta)\sigma_y+V\sigma_z],
$$
where $t$ is ...
5
votes
0answers
34 views
Help with understanding topologically-protected edge states in domain wall systems
Let's say that I have a simple domain wall system for the following Hamiltonian with added on-site potential $M(x)$:
$$
H(k,M)=-t \sum_{\delta} [\cos(k\cdot\delta)\sigma_x-\sin(k\cdot\delta)\sigma_y+M(...
5
votes
0answers
58 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 ...
7
votes
0answers
49 views
What are some types of topologically-relevant band degeneracies in contemporary 2D condensed matter research?
Cross-posted the question here: https://physics.stackexchange.com/q/633457/49107
In the study of 2D condensed matter systems, I have seen several kinds of band degeneracies. I call 'bands' the ...
15
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
364 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 ...
9
votes
1answer
85 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
70 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
56 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 ...
9
votes
1answer
266 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 ...
4
votes
0answers
42 views
Why does numerical computation of Berry curvature give me 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
37 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
66 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
43 views
Value of density of state effective mass and transport effective mass to calculate conductivity
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
529 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 "...
4
votes
0answers
22 views
Doubt in how dynamic strain aging and static strain aging are different from each other in its effect and phenomenon
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
41 views
A doubt about extended dislocation
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 ...
11
votes
1answer
97 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
37 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
66 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 ...
8
votes
1answer
64 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
468 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
463 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
336 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
203 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
59 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
44 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
54 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
95 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
150 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
278 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
55 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
1k 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
234 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 ...
16
votes
1answer
200 views
Difference between potential energy, free energy and Coulomb energy in solid state physics
I often encounter terms such as (Helmholtz, Gibbs) free energy, potential energy and total energy when describing the energy of a physical system at atomic level. Sometimes I stumble upon Coulomb ...
11
votes
2answers
239 views
How to convert Unified Pseudopotential Format (UPF) into Ultrasoft Pseudopotential (USPP) format?
I am working on DFT code having plane wave along xy axis and bspline in z direction. For calculating the properties of TMD materials, spin orbit coupling must be included but i did not find fully ...
13
votes
2answers
510 views
How much does the initial geometry affect the final geometry in optimization calculations?
This might be a stupid question but to what extent will the initial configuration of a bulk phase geometry optimization calculation affect the final geometry? Most places say to start with ...
8
votes
1answer
381 views
2D Brillouin zone generator
There are several pages where you can find scripts/simulations to generate the first Brillouin zone for square and hexagonal 2D lattices.
I wonder if there is a tool to generate the Brillouin for ...
15
votes
0answers
117 views
How to find the projected Hamiltonian for lowest flat-band in general?
In [1], starting with the bosonic Hamiltonian (Eqn. 1) for the dice lattice model with half flux density (with Ahronov-Bohm phases incorporated),
\begin{equation}
H=-t\sum_{\langle j,\mu\rangle}(a^\...
9
votes
1answer
262 views
What is the difference between U(1) and O(2) symmetry?
To my understanding, they both refer to circular symmetry. I know U(1) is the complex plane, and I think O(2) is real numbers. I have seen them used more or less interchangably, but is there actually ...
19
votes
2answers
330 views
What significant matter modelling methods are implemented in commercial software, for which there is no freeware alternative?
There is an ever-growing list of freeware and open-source software for solid-state physics and quantum chemistry.
But many commercial programs still thrive, even in 2020, and their cost can be in ...
15
votes
1answer
62 views
What are good resources to study crystallographic defects in different dimensional systems and their topological dimensionality?
I wonder if there are any books or resources that may address one or more of the following questions:
What kinds of defects are important for topology? Especially crystallographic defects.
How do ...
20
votes
1answer
141 views
What class of materials are closest to realizing the tunable coupling Hamiltonian?
From a physics point of view, there is an effective (approximation to second-order coupling Jaynes-Cummings) Hamiltonian of the form [1]
\begin{equation}
H=\sum_j\omega_j(t)\sigma_j^z+\sum_{\langle i,...
17
votes
1answer
133 views
What exactly is a topological insulator and how to recognize one from band structure?
Four years ago, the Nobel Prize in physics was awarded for "for theoretical discoveries of topological phase transitions and topological phases of matter." In line with this, I heard of topological ...
