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24 views

Choosing a basis state for density functional theory calculations

How do we choose basis set of wave functions for expanding the eigenfunctions of the kohn-sham equations? I mean given a material,what should i look for in order to choose my basis functions?
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1answer
59 views

Doped semiconductor: “what if all donated electrons are gone?”

I have trouble understanding conductivity of a n-doped semiconductor in the band theory. I know that donator atoms carry one excess electron that can enter the conduction band easily. If this happens,...
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1answer
210 views

Relation between band structure, dispersion, density of states, and the Fermi energy and Fermi level

Despite the long title, this question is mostly qualitative (although I am interested in quantitative results if possible). Say you have an electronic band structure (energy as a function of "k") for ...
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2answers
131 views

Density Functional Theory (DFT) calculation for metals

Why is DFT not used in calculating electronic structures and properties of metals? I know DFT calculations are not accurate for metallic structures. Can someone explain why?
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0answers
25 views

Band structure and k vectors

If there is a restriction on the allowed states (k vectors) for a system, ie the no of states is equal to twice the number of unit cells in the crystal.. why do we plot k continuously on the x axis? ...
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0answers
48 views

element effect on quantum dot band gap

Main Question: Why do Au QDs have quantum confinement effects which change optical behavior from the bulk Au, whie certain other elements (such as Fe) are typically not shown to have the same ...
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0answers
21 views

Optically access a single valley in indirect semicondutors

An indirect semicondutor has an energetic minimum of its band structure at a point different from the $\Gamma$ point. But, there are multiple of them. Silicon for example has its band minimum at the ...
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1answer
59 views

Why dopant energy levels differ from one material to another?

Dopant levels in Si, Ge and GaAs are very different from each other. Even "similar" materials such as Si and Ge exhibit different dopant energy levels. (source: Pierret, Advanced Semiconductor ...
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1answer
58 views

How can a material be conductive and transparent at the same time?

Transparent conducting films for example. On one hand, the band structure of transparent materials must have a large enough HOMO-LUMO separation. On the other hand, conducting (metallic) materials ...
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0answers
89 views

Materials for use in a solar cell

In a solar cell, photons of the incident sunlight supply energy for excitation of electrons - a process which generates electron-hole pairs which can move under the influence of the electric field of ...
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0answers
48 views

Band-gap for solids with isoelectronic atoms

Isoelecronic atoms have same number of electrons but different nuclear charge. It is said that many of the chemical properties of these elements are equal or at least similar. Can I form solids with ...
3
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0answers
88 views

What is the effective electron mass in a plasma?

Is there a way to calculate the effective electron mass in plasmas? Effective electron mass is usually defined as varying from the vacuum electron mass in solid state physics. However, momentum ...
2
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2answers
92 views

Do metals *really* conduct at zero temperature?

The questions is mostly in the title, but might expose another of my misunderstanding of the band structure of solids and how that leads to metals and insulators. If we have a solid, and the fermi ...
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1answer
155 views

Density of States in NOT Free Electron Gas

I think that I understand how the density of states works for a free electron gas. It is effectively just a conversion factor between summing over values of k and integrating over values of E. If you ...
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0answers
35 views

determination of electron dispersion curves

I am somewhat new to quantum physics and I am studying electron dispersion band structures of SiC like the one here I want to know what spectroscopic techniques/methods or if they are spectroscopic ...
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2answers
137 views

Density Functional Theory (DFT) tutorial guide

I am going to start learning about DFT calculations. Could anyone advise me the best starting point for that? Simple example guiding tutorial with explanations would be great. Any input would be good....
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0answers
36 views

What is the “point” of STM?

Scanning tunneling microscopy (STM) measures density of states (DOS) in a sample. But angle-resolved photoemission spectroscopy (ARPES) measures the bandstructure $E(\mathbf{k})$ in a sample, from ...
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0answers
21 views

What is the meaning of band structure in the case of amorphous materials?

A consistent band structure is expected in crystals, because "everything is uniform". Theoretical calculations of band structure are also based on infinite lattice. In amorphous materials, however, I'...
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0answers
42 views

How to determine the Fermi energy in Schottky barrier FET(SB-FET) channel?

The structure of Schottky Barrier FET(SB-FET) is almost the same with MOSFET. The difference between SBFET and MOSFET is the contacts change from Ohmic contacts to Schottky contacts. I know the way ...
2
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1answer
105 views

how do electrons in 2 separate atoms change its energy level when atoms come close together to form molecule?

The question is just as the title. It's said that electron must receive a specific amount of energy in order to go or drop to another energy level. So how can electrons of separate atoms which have ...
2
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1answer
46 views

at $T \approx 0 \, \text{K}$, will all energy levels within the electronic band structure be occupied up to a certain level?

I saw this from the script of my teacher that I don't understand what does it mean If we cool down a crystal to an absolute temperature of T ≈ 0K, all atoms of the crystal will exist at their ...
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0answers
86 views

Analysis of a Fermi surface

The following image shows the Fermi surface of Pb, plotted with XCrySDen. I have some difficulties in uderstanding the characteristics of that Fermi surface, in particular how to distinguish the ...
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0answers
51 views

what can be the BG and dielectric constant of monolayer MoS2 in semiconducting state (2H) and in metallic state (1T)

Monolayer MoS2 is a semiconductor that can undergo an MIT (Metal to insulator) or semiconducting state to insulating state transition. The semiconducting state is referred as 2H State and the metallic ...
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0answers
113 views

Band Structure from Fourier Transform Solution of Dirac Comb

I have use Fourier transforms to solve the Schrödinger equation for an attractive Dirac-$\delta$ comb potential of the form $$ V(x) = -\alpha \sum_{j = -\frac{N}{2}}^{\frac{N}{2}} \delta \left( x - \...
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1answer
27 views

Silicon parabolic dispersion for X minima

I am constructing a minimal model of the silicon conduction band minima for a monte-carlo program. Assuming the six equivalent bands are parabolic and spherical, since the conduction band minima lie ...
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0answers
34 views

Can I use an IV curve alone to differentiate between metallic, semiconducting and insulating materials?

Assuming the size of the bandgap is expressed as resistance in the IV curve, could I tell between metals, semiconductors an insulators by only doing an IV sweep? For example very high slopes (large $\...
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1answer
50 views

What's the difference between semiconductor and insulator (besides band gap)?

The typical classification of electronic materials is metal-semiconductor-insulator. Is there any actual difference between a semiconductor and an insulator, besides the size of the bandgap?
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1answer
140 views

Connection between fermi velocity and mean (square) velocity of diffusion current

Is there any connection between $v_{F}$ and the $<v^{2}_{diff}>$, lets say for electrons in metals? I have come to a conclusion, that they are the same order of magnitude and their equivalence (...
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3answers
143 views

Why is there a band structure for strongly correlated systems?

The existence of band structure of a crystalline solid comes from the Bloch theorem, which relies on the independent-electron approximation. Why do people still talk about the band structure for a ...
1
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1answer
98 views

What is the physical meaning of an electronic system evolving adiabatically through a closed path?

I am trying to understand Physics behind the Weyl Fermion in Condensed Matter Systems. Electrons show Weyl fermionic behaviour in the vicinity of so called 'Diabolical Points' in the band structure. ...
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1answer
38 views

How do phonons affect the work function?

How do phonons affect the work function? Could phonons that are directed towards a single atom, such as in a body-centered cubic crystal, increase the amount of thermal excitation and thus decrease ...
3
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2answers
171 views

Are there measurable quantities which directly depends on the Fermi velocity?

The dispersion relation of electrons in, for example, graphene exhibits Dirac cones. The dispersion relation of a Dirac point at $\mathbf{k}=\mathbf{K}$ is linear in the momentum magnitude: $$E=\pm ...
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0answers
35 views

Do the band lines along high symmetry points contain all the information of the first Brillouin zone?

When calculating the electronic structure of solids, one usually plots the band structure along a certain set of paths that connect high symmetry points in the first Brillouin zone(IBZ). I wonder ...
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2answers
559 views

Why are band maxima / minima often (always?) at high-symmetry points?

(inspired by this question.) In every semiconductor that I can think of, the valence band maximum and conduction band minimum are at a high-symmetry point in the Brillouin Zone (BZ). Often the BZ ...
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7answers
2k views

Quantization vs. continuous energy levels

I still don't get what it means for atomic energy levels to be continuous or quantitized (incontinuous). Clearing this up will really help me. Also, can anyone tell me why energy levels in solids are ...
0
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2answers
145 views

Conduction bands and Valence Bands, so do electrons really exist in Conduction bands?

My understanding is that conduction bands are energy bands created from the electrons in the valence shells/bands absorbing energy to jump to the next level (is this true)? Now, do the conduction ...
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1answer
162 views

What is the physics behind “Bulk-edge correspondence”?

There is a frequently mentioned concept in the field of topological insulator called "bulk-edge correspondence" or "bulk-boundary correspondence", which basically gives the relationship between the ...
2
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1answer
70 views

DOS integral when surface is not closed

According to the density of states (DOS) formula $$\rho(\varepsilon)\propto \int_{\varepsilon=\text{const}}\frac{dS}{|\nabla_k \varepsilon_k|}$$ Since there is an integral on the constant energy ...
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0answers
62 views

DOS behavior of Van Hove singularity in a line

When there are some points in momentum space give $|\nabla_k \varepsilon_k|=0$, they are called Van Hove points and give singularity in the desity of states (DOS). But what if $|\nabla_k \...
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0answers
211 views

DOS of Van Hove singularity in 2D square lattice tight binding model

For the simplest example, 2D square lattice tight binding model gives the energy band as $$\varepsilon_k=-2t(\cos k_x+\cos k_y) \, .$$ We know that $\vec{k}=(0,\pi)$ and related momentum points are ...
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0answers
129 views

How to get DOS of Van Hove singularity using quadratic dispersion relation

Take 2D case for example. We can first get the area in momentum space for all $k$ that satisfy $E_0<E(k)<E $, say $S(E)$. And the density of state (DOS) is $\rho(E)=\frac{\partial S(E)}{\partial ...
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0answers
34 views

How to get the asymptotic expression of DOS near Van Hove singularity [duplicate]

For the simplest example, 2D square lattice tight binding model gives the energy band as $$\varepsilon_k=-2t(\cos k_x+\cos k_y) \, .$$ We know that $\vec{k}=(0,\pi)$ and related momentum points are ...
1
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0answers
158 views

kp theory of QW band structures in envelope function approximation

I am currently trying to calculate wave functions and energy dispersions for quantum well heterostructures. The kp method is my choice to do that. I already calculated band structures for bulk ...
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0answers
128 views

Relation between energy band gap and atomic number

Is there any relation between energy band gap in group4 elements and their atomic numbers? It might be just a trivial observation but I noticed How from Carbon to Germanium the band gap went from 5....
0
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1answer
30 views

Are there electrons in the electron energy levels that are created due to doping in N type semiconductors?

I was going through this article.There it is mention that The addition of donor impurities contributes electron energy levels high in the semiconductor band gap so that electrons can be easily ...
2
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2answers
88 views

Why are reciprocal lattice vector periodic, and time-frequency not?

k-space vectors are related to each other by $k=k'+G$, where $G$ is the reciprocal lattice vector $G=2\pi/a$. This means that the frequency of oscillation in real space of a plane wave $e^{ikx}$ is ...
2
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1answer
165 views

Is Chern-number for free fermion system always limited by total band number, i.e. number of orbits with a unit cell?

If so, how to see that? Also I think it has been proven that the total Chern-number for free fermion system is 0? If you know how to prove it, please make some comment or hopefully a sketch of proof....
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0answers
56 views

Why graphene's substrate is important

I just have some feelings that somehow it is important what specific subtrate is used to grow graphene monolayer on. Some substrates are better, another ones are not so good. But I cannot completely ...
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1answer
486 views

Understanding electronic band structure diagrams

Currently I'm trying to understand electronic band structures such as depicted below: And following questions were arisen. Why are there multiple lines in valence side and conduction side? Where ...
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0answers
105 views

Problem with energy bands

I am getting confused by the energy bands. As far as I know, the outermost shell of an atom is called valence shell. The electrons residing in that shell participate in reactions and conduction of ...