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I want to understand the electronic band structure diagram of the following image, corresponding to $\text{MoS}_2$ (TMD):
I read about DFT (density functional theory).
DFT is based on solving the Schrodinger equation for a set of atoms. Through the Born Oppenheimer approach, it is possible to de...
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From Statistical Mechanics obtain an expression for the heat capacity of a solid is given by1:
\begin{equation}
\tag{1}
{C_V}\left( T \right) = k\int\limits_0^\infty {\frac{{{{\left( {uv} \right)}^2}{e^{uv}}}}{{{{\left( {{e^{uv}} - 1} \right)}^2}}}g\left( v \right)dv}
\end{equation}
with $u=h/kT...
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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 as eroded coastlines or snowflakes) in which similar patterns recur at progressively smaller scal...
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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 (nanostructures, crystals, etc.).
Any time I submit a manuscript in the biological area, either the editors...
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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 glide planes, which I marked in the figure (see blue rectangles). However, more than three glide...
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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 the cold zone. This is visible in the Excel chart I obtained from the practice, in which I place...
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Studying magnetic systems, two frequently used approximations are the Heisenberg and Ising models (a discussion about these approximations can be read here):
\begin{equation}
\tag{Heisenberg}
\hat{H}_H=-\sum_{\langle i j\rangle}J\hat{S}_i\hat{S}_j
\end{equation}
\begin{equation}
\tag{Ising}
\hat{...
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This question is related to other one here in the MatterModelingSE:
Is it possible to calculate/estimate the value of the J parameter to be used in the Heisengerg/Ising hamiltonians?
Here J is the exchange interaction parameters between two nearest-neighbor spins using in Heisenberg and Ising h...
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I have recently been working with non-collinear antiferromagnetic systems. I understand that, in order to obtain spin density, one must obtain the electron density in one configuration of spin and subtract the electron density in the other configuration.
I am unsure as to how to go about this in ...
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I work with magnetic materials and I haven't found a way to automatically plot structures with their corresponding magnetic moments. For this specific project I am using VASP. I am trying to plot something like this:
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In Jensen's Introduction to Computational Chemistry it says that the total non-relativistic Hamiltonian operator, transformed to the center of mass system, can be written, in atomic units, as
$$ \hat{H}=\hat{T}_N+\hat{H}_e+\hat{H}_{mp} $$
where $\hat{T}_N$ is the kinetic energy of the nuclei, $\...
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Q: How to convert Unified Pseudopotential Format (UPF) into Ultrasoft Pseudopotential (USPP) format?
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I have been assigned a project on the generation of a force-field of Al (aluminum) for a LAMMPS potential.
I have no idea how to proceed and what to do next. Can anyone please let me know how should I proceed further?
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I would like to know what are the different types of pseudopotentials, the pro and cons, and what properties can/cannot be calculated with them?
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If you do a bibliography search about the codes used in matter modeling, you will find a large list.
I played with a few of them (both free and commercial) and one of my findings is that the properties they can calculate are different, even being important properties. I am aware that they used di...
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I want to calculate the density of states of GaAs conduction band (preferably each valley like Gamma, L and X). Is there any software available where I can easily generate DOS?
Has the DOS of GaAs been studied previously?
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I am interested in studying material heat transport using Density Functional Theory. Searching, I found a work1 about using ab initio equilibrium molecular dynamics (AIMD) as implemented in QuantumEspresso (QE) software.
I already used/tested QE for other simpler calculations and I found it very ...
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The image below refers to a phenomenon that occurs in TMDs (transition metal dichalcogenides) that allowed the development of valleytronics. Why are there separate bands of different colors in this image (some with red on top and blue on bottom and others with blue on top and red on bottom)?
Fig...
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I want to draw the energy ($E$) diagrams for a simple cubic cell of parameter $a$, where each atom provides two electrons for the almost free electron levels for planes [100], [110] and [111].
I calculate $k$ for the first Brillouin zone:
$k_{\text{ first Brillouin zone}}=\frac{\pi}{a}=\frac{3,14...
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Many problems in Computational Physics need the use of random number generators. When studying magnetic materials using the Heisenberg/Ising hamiltonians (related questions about them can be seen here, here and here), one of the must used tool is the Metropolis method1.
The Metropolis method can ...
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Previous questions (here, here and here) were about modeling magnetic homogeneous systems using Heisenberg and/or Ising hamiltonians:
\begin{equation}
\tag{Heisenberg}
\hat{H}_H=-\sum_{\langle i j\rangle}J\hat{S}_i\hat{S}_j
\end{equation}
\begin{equation}
\tag{Ising}
\hat{H}_I=-\sum_{\langle ij\r...
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I would like to demonstrate that the two-band Hamiltonian is given by the following formula:
\begin{equation}
\hat{H}_0=at(\tau k_x\hat{\sigma}_x+k_y\hat{\sigma}_y)+\frac{\Delta}{2}\hat{\sigma}_z-\lambda\tau\frac{\hat{\sigma}_z-1}{2}\hat{s}_z \tag{1}
\end{equation}
where $\tau=\pm1$ is the valley...
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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 with is how to determine the phase transitions based on a phonon band structure with such imaginar...
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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 curvature: "Berry curvature $\Omega(\mathbf{\lambda})$ is simply defined as the Berry phase per unit area in ($\l...
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I am trying to understand the Berry phase through the evolution of a system that evolves adiabatically.
Schrodinger's equation is:
\begin{equation}
H(\lambda)|n(\lambda)\rangle=E_n|n(\lambda)\rangle \tag{1}
\end{equation}
where $n$ labels the eigenstates. If $\lambda$ doesn't change with time, th...
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The wave function for the adiabatic approach is as follows:
\begin{equation}
|\psi(t)\rangle=e^{i\phi(\lambda(t))}e^{-i\gamma(t)}|n(t)\rangle \tag{1}
\end{equation}
where $e^{i\phi(\lambda(t))}$ is the geometric phase or Berry phase and $e^{-i\gamma(t)}$ is dynamic phase.
Berry phase has the foll...
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What does the quantum anomalous Hall phenomenon consist of?
I am studying the transition metal dichalcogenides (TMDs) and I have seen webinars and articles that said that these materials exhibited the anomalous quantum Hall effect related to the curvature of Berry, which changes the speed of elec...
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I want to represent parallel transport as in the following figure, but next to this figure I would like to place a diagram with the two arrows (of the initial state and of the final state that are present at the top of the spherical surface) and the angle between them, to see better and put more ...
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High-throughput density functional theory (DFT) calculations are used to screen for new materials and conduct fundamental research in materials science and materials innovation. It involves computations on tens of thousands of compounds, and such a scale demands unique calculation and data manage...
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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 other 2D lattices like the tiles presented here and here.
PS: I am aware that not all the tiles can...
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For the choice of k-mesh we have few options like:
Monkhorst-Pack,
Chadi-Cohen,
Gamma-centered mesh,
etc.
What are the different types of k-mesh and what are their pros and cons?
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A Brillouin zone is defined as a Wigner~Secitz primitive cell in the reciprocal lattice [1,2].
The construction of the first Brillouin zone for two different 2D lattices are shown below:
The construction procedure for 3D lattices is basically the same as for 2D lattices. In the image below, ...
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Since the beginning of the century, Wien2K has proven to be a very powerful player in computational condensed matter and materials physics.
Wien2K is an all-electron periodic DFT code based on the Augmented Planewave + Local Orbital [APW+lo] method, and also widely known as Full-Potential - Linea...
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I'm trying to simulate a graphene flake with its edge C atoms saturated by H atoms, in a temperature ramp from 300 K to 1600 K, using LAMMPS and the AIREBO potential proposed by Stuart et al. in 2000.
The problem is when the temperature is close to 500 K the C-H bonds start breaking and at 1600 K...
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A few years back, I performed a few calculations of metallic slabs using VASP and the Atomic Simulation Environment (ASE). I'm by no means an expert, but I noticed that the calculations were very CPU intensive e.g. ~24 cpu-hours (in parallel) to get a single energy point and gradient calculation....
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In order to do DFT calculations of metallic alloys, the start point is a supercell, whose atoms are changed to match the desired stoichiometry. Gold and Silver, for example, both have FCC structure. In Quantum-ESPRESSO, we can both tell to the code the Bravais lattice (ibrav parameter) and specif...
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I am studying a material which was first discovered in the early 1960s. It was reported then that it crystallized in the hexagonal $P6_3/mmc$ space group. Recently the material was synthesized again and found that it posses $P6_3mc$ symmetry. My own DFT calculations and another published work fin...
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I am using VASP package to model a material that has fractional site occupancies. An appropriate supercell (cif) was generated using supercell package and converted to POSCAR using VESTA. Then the structural relaxation was performed. Now I have the relaxed structure (CONTCAR) and I want to analyz...
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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 permit mirror plane symmetry and / or inversion symmetry. [16] In the macroscopic bulk crystal, or...
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I am seeking some models or references on how to couple or what to take into consideration while coupling first-order phase transition (for magnetic systems) and second-order phase transition regarding order and disorder in these systems.
I am attaching a link for one such system https://www.natu...
This is something I don't understand comprehensively. Also aren't default external pressure values equal to zero for DFT codes?
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