Questions tagged [symmetry]
Questions relating to symmetries and symmetry groups encountered in materials modeling.
44
questions
7
votes
1answer
71 views
Symmetry group of p-benzoquinone
I am trying to calculate the UV-visible spectrum of p-benzoquinone. In the literature, the point group of p-benzoquinone is $D_{2h}$, but when I optimize this molecule in the ground state with ...
6
votes
1answer
126 views
About LaCrO3 space group stability
I found two space groups of $\ce{LaCrO3}$ material Pnma and Pm-3m. If someone is familiar with this material, please help to understand which phase is more stable. what are the factors that determine ...
4
votes
0answers
29 views
Do the VBM and CBM have to be on the high symmetry point? [duplicate]
I am trying to generate the band structure of a slab, a lot of tutorials tell me that I need to generate the high symmetry K point path, but I am wondering that if the VBM and CBM have to be on the ...
5
votes
0answers
49 views
Is the formula of Dyson orbital independent of whether there is degeneracy or not in the HOMO of the neutral?
Dyson orbital is defined as
$$
\textrm{Dy}(x) = \int dx_1 \ldots dx_{N-1} \, (\Psi^+(x_1,\ldots,x_{N-1}))^* \, \Psi^0(x_1,\ldots,x_{N-1}, x)
$$
where $\Psi^0$ and $\Psi^+$ are the total wavefunctions ...
9
votes
1answer
113 views
Should one consider the spatial degeneracies of the electronic state while calculating the Gibbs free energy?
The Gibbs free energy of a molecule is generally expressed as a sum of translational, rotational, vibrational, electronic and nuclear contributions. The electronic contribution $G_{elec}$ is formally ...
5
votes
0answers
71 views
Spacetime translation of Noether's current density
I've heard so many times that spacetime translation invariance is assumed when we speak about Noether's current density. Could someone explain to me, why is that so? What if we don't assume it?
To be ...
7
votes
1answer
92 views
Case study : Symmetry operation between VASP and Quantum espresso
I am doing simple scf calculation to find similarities in the output of VASP and QE.
Recently, I encounter an interesting case. ...
9
votes
1answer
339 views
Proposing a 2D quasicrystal; what are the necessary and sufficient conditions? (If it looks like a duck and quacks like a duck, or...?)
Quasicrystals show repeating motifs or patterns but are not periodic. And yet their Fourier transforms invariably demonstrate a pattern of sharp peaks revealing that there is still an underlying... ...
5
votes
0answers
59 views
Space group will not change in VESTA
I have one unit cell of 16 atoms (4 formula unit cells) 2x2x2 unit cells. I want to construct the supercell with 32 and 64 atoms. I went in the transform and I changed the rotation matrix 4x2x2 and ...
6
votes
0answers
40 views
Constructing the symmetry operator from k.p Hamiltonian [closed]
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 ...
3
votes
1answer
76 views
How to do a proper relaxation of the multicomponent structure?
I have a beta Ti (Space Group 229) structure with 16 atoms, I prepared 15 disordered TiNb structures with 5 atoms of Nb. I did it using VASPKIT. However, before the ...
4
votes
1answer
61 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 ...
10
votes
1answer
119 views
Quantum ESPRESSO ph.x output
I wanted to calculate the normal modes of some particular material using the Quantum ESPRESSO. Everything went fairly well, but there is a couple of lines in the output that I do not understand. In ...
9
votes
0answers
72 views
Crystallography: How to sample *unique* structures from configuration space? (binary alloy supercell) [closed]
I'm working with a binary alloy system (call it 'AB'), and I'd like to generate a few unique configurations for DFT purposes.
My primitive cubic unit cell consists of 4 atoms; i.e. 4 positions. Thus, ...
10
votes
0answers
62 views
How to generate a complete set of doped (substituted) structures? [duplicate]
I'm trying to analyse doping in a certain material in low concentrations. I'm approaching the problem by taking crystallographic unit cell of that material, then expanding that to a 2x2x2 supercell ...
11
votes
1answer
362 views
Does the spin polarised DFT calculation mean broken time reversal symmetry?
Recently, I have got to learn that if time-reversal symmetry and inversion symmetry are present simultaneously in the system we have the following conditions on energy of Bloch's states:
$$E_{n,\chi }(...
17
votes
2answers
581 views
What are good tools for visualizing glide planes and screw axes?
While there are a few tools for visualizing crystal structures, I'm particularly curious to know tools for visualizing space group symmetry, including:
screw axes
glide planes
I teach a class on ...
7
votes
0answers
70 views
Construct a parity operator at a TRIM point? [closed]
I want to calculate the band parity at some TRIM (time-reversal invariant momentum) point in Brillouin zone. Parity was defined as the eigenvalue of the inversion operator. My question is how to ...
5
votes
1answer
171 views
How do I extract the wave function from a VASP calculation?
We can obtain a energy band structure of a crystal from a DFT calculation in Vasp. Each point in each band represents an energy eigenvalue with a corresponding wave function from the Schrödinger ...
5
votes
0answers
140 views
What's the information contained in a character table of a group? [closed]
This question has an answer on the Chemistry Stack Exchange: Understanding group theory easily and quickly.
Anyone wishing to add alternative or additional perspectives that aren't already covered in ...
11
votes
3answers
791 views
How to build a nanocluster?
What are the software tools (if possible open source) or methods we can use for constructing a nanocluster, most preferably with high symmetry such as icosahedron, octahedron, cuboctahedron etc. ?
8
votes
2answers
209 views
What will break the time-reversal symmetry?
Specifically, I am interested in the time-reversal symmetry $(\mathcal{T})$ in quantum mechanics. The $\mathcal{T}$ is considered as an anti-unitary operator, namely:
$$\mathcal{T}\psi(\vec{r},t)=\psi^...
11
votes
3answers
139 views
Rotation of crystal structure to match another structure of the same compound/polymorph
Say, I have two crystal structures of a particular organic molecule, the crystal structures are basically identical, apart from a rotation and redefinition of the lattice vectors/angles, a simple ...
9
votes
1answer
196 views
PT-symmetry leading to spin-degenerate band structures
I am trying to understand the fundamental physics of a kind of problem. I will introduce a specific example and then list some of the broader qualms I hold. I have observed many band structures, be it ...
10
votes
1answer
191 views
Nematicity in superconductors
It seems to me that the definition of "nematic phase" is quite chamaleonic.
Quoting from its first definition [Nature 393, 550 (1998)] for a 2-dimensional square lattice "The nematic ...
9
votes
1answer
139 views
Topological order in Weyl Semimetal
Is the topological phase in a Weyl semimetal is intrinsic or symmetry protected? How can we realize that?
If symmetry protected, which symmetry protects the topological phase of non-centrosymmetric ...
12
votes
1answer
156 views
Why linear response is absent in a non-centrosymmetric system with time reversal symmetry?
In this paper, it is mentioned that a non-centrosymmetric system with time-reversal symmetry doesn't have a linear response. It is actually a consequence of the Onsager reciprocal theorem.
But I didn'...
10
votes
1answer
268 views
How to analyze the band symmetry with Quantum ESPRESSO?
This question is related to this paper: J. Phys. Chem. Lett. 2017, 8, 13, 2999–3007
The above figure shows symmetry analysis for the band structure. The author writes:
The band symmetry and parity ...
5
votes
1answer
213 views
Is there a difference in performance when the symmetry is specified via ibrav in Quantum ESPRESSO?
I have been using cif2cell for converting CIF files into quantum ESPRESSO input files. But cif2cell always keeps the ibrav value to be zero and indicates the CELL_PARAMETERS. As per the quantum ...
12
votes
1answer
117 views
What does it mean to assign group operations to distinct sets for space groups?
I am trying to understand space groups in crystallography. In International tables for crystallography, for a nonsymmorphic space group, they list some symmetry operations. 8 of them are listed under ...
9
votes
1answer
108 views
Partial density of states in random solid solutions
This question comes as a follow-up to https://mattermodeling.stackexchange.com/a/2214/116; nonetheless, it is relevant on its own as well.
To designate a particular crystal structure to a random ...
9
votes
1answer
143 views
Why does mcsqs change the space group of generated SQS?
I made a binary special quasi-random structure (SQS) using mcsqs (distributed as part of the ...
8
votes
0answers
97 views
How to classify ionic and covalent excited-states?
In spectroscopy it is common to describe excited-states as ionic or covalent.
I understand the concept on a toy model e.g. $\ce{H2}$ with a minimal basis set
\begin{align}
\Phi_0 &= [\chi_A(1) + \...
11
votes
2answers
471 views
Effect of ISYM tag on Partial Density of States (VASP version < 6)
This is from the entry for LORBIT in the VASP Wiki.
For LORBIT >= 11 and ...
8
votes
1answer
388 views
Inversion symmetry in 2D materials
Transition metal dichalcogenides (TMDs) are composed of three atomic planes and often two atomic species: a metal and two chalcogens. The honeycomb, hexagonal lattice has three fold symmetry and can ...
9
votes
1answer
292 views
Get fractional coordinates from special Wyckoff positions
I'm trying to get the fractional coordinates for Mo and S, for MoS$_2$-2H, where 2H means the phase. MoS$_2$-2H is a bilayer, in which each layer is separated from each other by Van der Waals forces. ...
8
votes
0answers
49 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 ...
19
votes
4answers
400 views
How is group theory used to deduce which of these integrals are equal to 0?
The number of all two-electron integrals:
$$
\tag{1}
\langle \phi_1 \phi_2|\phi_3\phi_4 \rangle = \int d^3\mathbf r' \int d^3\mathbf r'' \, \phi_1(\mathbf r'') \, \phi_2(\mathbf r') \frac{1}{|\mathbf ...
17
votes
2answers
650 views
How to deduce phase transitions from a phonon calculation?
I came across the concept of using phonons to establish a material's dynamical stability, based on whether or not imaginary frequencies are present in its phonon band structure.
What I am struggling ...
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
225 views
Dealing with symmetry of ordered primitive cell during DFT structure relaxation
I have a large disordered cubic structure that I would like to do AIMD on to look at cation diffusion. I found the primitive cell and then ordered it to create several configurations. I will then ...
19
votes
1answer
1k views
Is the number of possible Bravais lattices a mathematical fact?
Almost anyone that has taken a Solid State Physics course will know, that any 3D crystal must be in one of the 14 Bravais lattices due to symmetry operations and space filling.
In 2015, a paper was ...
14
votes
1answer
166 views
conceptual problem about the energy band along the High symmetry point in the Brillouin zone
When we calculate the band structure of certain material, we only have to calculate the value along the high symmetry point which enclose the Irreducible Brillouin Zone. Why the information lie in the ...
9
votes
1answer
536 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 ...
