Questions tagged [condensed-matter]

For all matters related to condensed matter physics.

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Where/when did the fields of Operations Research and Spin Physics or Molecular Dynamics begin to cross-pollinate?

Operations Research is a field of mathematics in which optimal or near-optimal solutions are sought for complicated problems. In the modeling of materials, we often optimize Ising models, in which the ...
Nike Dattani's user avatar
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22 votes
2 answers
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Is there a list of all universality classes for phase transitions with examples of each?

I've often had this problem: I have a model that has a phase transition in it, but I don't know what universality class it falls into or what the universality class is called. Is there anywhere on ...
taciteloquence's user avatar
20 votes
1 answer
156 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,...
Siddhant Singh's user avatar
20 votes
1 answer
181 views

What is the importance of electron interaction on dielectric response of crystals?

After obtaining the Kohn-Sham orbitals from a plane-wave-based self-consistent-field calculation, the dipole matrix elements could be calculated in order to determine electro-optical properties such ...
Anibal Bezerra's user avatar
19 votes
2 answers
384 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 ...
Matthew W. Noble's user avatar
19 votes
1 answer
2k 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 ...
Achintha Ihalage's user avatar
17 votes
1 answer
4k 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 ...
JensenPang's user avatar
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17 votes
2 answers
654 views

Software for solving quantum systems in 1D and 2D

I'm looking to solve quantum system in 1D and 2D consisting of a large number of sites. What are the pros and cons of each package, and which package is more suitable for what type of calculations? ...
explorer's user avatar
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17 votes
1 answer
311 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 ...
Verktaj's user avatar
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17 votes
1 answer
520 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^\...
Siddhant Singh's user avatar
16 votes
3 answers
1k 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 ...
epalos's user avatar
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16 votes
1 answer
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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 ...
Siddhant Singh's user avatar
15 votes
3 answers
3k 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 ...
Paulie Bao's user avatar
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15 votes
2 answers
283 views

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

Cross-posted on Physics.SE. 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 ...
KFC's user avatar
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15 votes
1 answer
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Functionals/basis sets optimized with respect to properties?

In general (at least for molecular calculations) basis sets and DFT functionals are fit to some high level calculation or experimental energy. It is speculated that an accurate energy will result in ...
Tyberius's user avatar
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14 votes
2 answers
599 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 ...
Cavenfish's user avatar
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14 votes
1 answer
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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 "...
tmph's user avatar
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14 votes
1 answer
143 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 ...
TribalChief's user avatar
  • 2,281
14 votes
1 answer
244 views

What are differences between Mott and Anderson transitions?

Can anyone please explain the differences between Anderson and Mott insulator-metal transition? I found some information in the book named "The_Physics_of_Amorphous_Solids".
Binh Thien's user avatar
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13 votes
3 answers
1k 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 ...
Alisufyan's user avatar
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13 votes
2 answers
884 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 ...
Raj Kumar Paudel's user avatar
12 votes
2 answers
899 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 ...
Jack's user avatar
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12 votes
2 answers
2k 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 ...
UJM's user avatar
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12 votes
2 answers
132 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 ...
Camps's user avatar
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12 votes
1 answer
309 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 ...
TribalChief's user avatar
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12 votes
1 answer
170 views

Why are condensed matter predictions considered on par with experiment, while structural biology modeling receives more skepticism?

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 (...
Camps's user avatar
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12 votes
0 answers
109 views

First principles calculations beyond s-wave BCS superconductors [closed]

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 ...
2ndQuantized's user avatar
  • 1,021
11 votes
3 answers
336 views

How does a beginner condensed matter theorist working on real materials, get up to speed?

I asked this on Physics.SE and got recommended here. More precisely, as a condensed matter theory PhD student, I am often overwhelmed by the wide variety of chemical formulas that experimentalists ...
Andrew Hardy's user avatar
11 votes
2 answers
961 views

Why the band structure of a slab is not smooth?

I am trying to calculate the band structure of a TiO2-Rutile slab, but the result I got is not very smooth, and the result shows it is an indirect gap material, but the bulk phase of TiO2-Rutile is a ...
Jack's user avatar
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11 votes
1 answer
450 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 ...
M_Fisher's user avatar
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11 votes
1 answer
304 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 ...
TribalChief's user avatar
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11 votes
1 answer
1k 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 ...
Thomas's user avatar
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11 votes
1 answer
124 views

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

Cross-posted here. Consider the usual simple 2-level gapless graphene Hamiltonian in momentum-space where the energy dispersion is degenerate/gapless at a Dirac point: \begin{equation}\tag{1} {\small ...
TribalChief's user avatar
  • 2,281
10 votes
1 answer
333 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 ...
Jack's user avatar
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10 votes
1 answer
644 views

Kramer's Degeneracy and Antiferromagnetism

How can one understand the concept of Kramer's Degeneracy for an antiferromagnetic system where spin-up and spin-down bands overlap due to net zero magnetic moment?
Shahid Sattar's user avatar
10 votes
1 answer
161 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 ...
Brian Lancaster's user avatar
10 votes
1 answer
2k 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 ...
taciteloquence's user avatar
10 votes
1 answer
347 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 ...
Atom's user avatar
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9 votes
1 answer
457 views

What software can I use for gas adsorption calculations?

We are from a new research group working on matter modelling. Currently our work has focused mainly on classical Molecular Dynamics (MD), Lattice Dynamics (LD) and ab-initio methods. For these, we ...
PBH's user avatar
  • 2,603
9 votes
1 answer
314 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 ...
TribalChief's user avatar
  • 2,281
9 votes
1 answer
259 views

Evaluating Seebeck coefficient using DFT

I am working with semiconductor materials using the SIESTA DFT package. I have tried the BoltzTraP2 software interface with SIESTA, however the results (Seebeck coefficient of MgO and Si) did not ...
PBH's user avatar
  • 2,603
9 votes
1 answer
216 views

How to identify localized surface states in the band structure

After calculating the band diagram of a structure, is there a way to identify localized surface states? I am working with Si nanowires with different cross sections. I want to determine the band gap ...
PBH's user avatar
  • 2,603
9 votes
0 answers
92 views

How does infinite DMRG work? [duplicate]

iDMRG or infinite-size density matrix renormalization group, is a common technique in condensed matter. It seems that usually people believe that it reliably captures infinite-size behavior. I have ...
taciteloquence's user avatar
8 votes
2 answers
278 views

Are there interesting applications of estimating the energy for generalizations of the Heisenberg model?

I consider that $H$ is a Hamiltonian describing a quantum system of $n$ spin-1/2 particles (or qubits). I assume it can be written as (the $\alpha_k^i$ are real coefficients): $$\tag{1}H=\sum_{i=1}^3 ...
Marco Fellous-Asiani's user avatar
8 votes
1 answer
313 views

Can deformation potential theory be applied to 2D and 1D systems?

I was pointed towards the use of the Deformation Potential (DP) theory to calculate the electron relaxation time in a previous question. However, I still have a doubt regarding its applicability to 2D ...
PBH's user avatar
  • 2,603
8 votes
1 answer
879 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?
Alisufyan's user avatar
  • 691
8 votes
1 answer
431 views

Screened Coulomb interaction and its direct Fourier transform

I have a question concerning the screened Coulomb interaction in periodic systems. Many first-principle DFT codes provide the possibility to compute linear response functions, such as the irreducible ...
franz's user avatar
  • 297
8 votes
1 answer
131 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 $M(x)$: $$\tag{1} H(k,M)=-t \sum_{\delta} [\cos(k\cdot\delta)\sigma_x-\sin(k\cdot\delta)\...
TribalChief's user avatar
  • 2,281
8 votes
1 answer
1k 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 ...
Camps's user avatar
  • 22.3k
8 votes
1 answer
235 views

How to numerically calculate quantum state distance using quantum metric?

In Ran Cheng's review of the quantum geometric tensor, eq. (11) gives the tensor as: $$ Q_{\mu\nu}=\sum_{n\neq 0}\frac{\langle\phi_0|\partial_\mu H|\phi_n\rangle\langle\phi_n|\partial_\nu H|\phi_0\...
TribalChief's user avatar
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