Questions tagged [density-functional-theory]

For questions about simulations using Density Functional Theory.

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Functional derivatives in DFT

Crossposted from Physics SE. I am studying density functional theory and I am currently dealing with manipulating the intrinsic free energy, $\mathcal{F}$, which is defined as $$\mathcal{F} = F - \int ...
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How to define ferrimagnetism in quantum Espresso

I would like to pick this problem from my previous post See link. I am clear about how to define antiferromagnetism in QE. Here I am with another issue. I am ...
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Determining conduction band minimum of a semiconductor

How can I determine the minimum of the conduction band of a semiconductor using DFT/VASP, or any other option?
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Why are method developments and new implementations not done much in Gaussian?

While I have seen many papers in which Gaussian is used in calculations, I have not seen any paper in recent times where new methods are implemented in Gaussian. The latest paper I could find ...
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How to do lattice optimization, encut optimization and Kpoint optimization in VASP?

What is the procedure to do lattice optimization, encut optimization and kpoint optimization in VASP? Thank you in advance.
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How to make ferro, feri and antiferro magnetic structure for QE

I have below &SYSTME information from my input file ...
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Can transmission spectrum value exceed 1 within bias window?

I'm trying to simulate a ZnO nanoribbon structure using TranSIESTA in the siesta package. When I performed the transport calculations, for a few bias points within the bias window, the transmission ...
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Nanowire Band Structure using Siesta DFT

I'm working with the Siesta DFT software, and managed to reproduce the band structure of bulk Si without any issues. However, when trying the same with a Si nanowire, the band structure looks nowhere ...
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Relationship between functional derivative and potential value at a position

Thanks to very helpful and detailed answers for my previous question, I understand the functional derivative of the energy with respect to the density. In addition, this functional derivative is equal ...
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477 views

Functional derivative of energy with respect to density

I have read the paper of "A bird's-eye view of density-functional theory [PDF]" and I have a question about the functional derivative of the energy by the density. I have found the following ...
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How can I be sure that I have found the conduction band minimum in DFT?

Let's say I want to find the electronic energy bands from DFT calculations in VASP along a chosen path in the Brillouin zone. Now, I want to make sure I choose a path that captures the conduction band ...
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transition dipole matrix element

When doing DFT calculations of periodic solids, from either $\mathbf{k \cdot p}$ perturbation theory or simply using the trick $\mathbf{r} \rightarrow i\partial_{\mathbf{k}}$, one can obtain $$ \...
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Electron interactions between different positions or different orbitals

When I consider the grid positions $r$ in a molecular system, I have a matrix, where each row can be regarded as an N-dimensional vector and each column can be regarded as a G-dimensional vector. In ...
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A mapping between effective potential and non-interacting electrons moving on the potential

From this question and answer, I understood the Hohenberg-Kohn theorem and found that there is a one-to-one correspondence between the external potential $V_\text{ext}$ and the electron density $\rho$ ...
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Why do I get negative charge density values in the core of atoms when I perform DFT calculations with PAW?

We are all aware of the fact that negative charge densities in the atomic cores are an artefact of Density Functional theory Calculations using Projector Augmented Wave (PAW) method. But what is the ...
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Ground State energy trick for many-body electronic structure calculations?

I am an outsider to this field, so I am not sure about the validity of my work below. Let us define the following Hamiltonian from DFT: $$ \tag{1}H_{ij} \psi_{ij} \equiv (-\frac{\hbar^2 \nabla_i^2}{2m}...
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HSE06+SOC calculation in VASP: How to remove false k-points?

I followed the steps mentioned in the answer of question: How to carry out HSE06+SOC band structure calculation using VASP but I found a zigzag band structure. Any idea how to remove false k-points in ...
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Density functional theory and oxygen spin

I would like to perform single-point/geometry-optimization/NEB calculations on systems involving both molecular oxygens and adsorbed oxygens. Reductions by hydrogens are also involved. I am still ...
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What is a Padé approximant?

I have been looking at using Goedecker-Teter-Hutter (GTH) pseudo-potentials and I came across the abbreviation PADE. I was wondering what this abbreviation actually stood for and how it is related to ...
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Is the exchange-correlation term in Kohn-Sham equation always positive or negative?

The potential terms of the Hamiltonian in the Kohn-Sham equation are the external, Hartree, and exchange-correlation terms, which can be written as: $V_{ext}(r) = - \sum_{i=1}^{M} \frac{Z_i} {||r - ...
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Interpretation of effmass module

Currently, I am trying to figure out the effmass module. I'm newly into effective mass stuff and I'm able to run it and generate effective masses. However, I'm facing some trouble understanding it. Is ...
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How to extract transition density cube from .fch file in Gaussian?

I have been trying to extract the transition density cube of a simple molecule, $\ce{H_2O}$. I did a regular geometry optimization and then TD-DFT calculation with a keyword ...
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1answer
111 views

One-to-one correspondence between electron density and external (Coulomb) potential

I calculated the electron density of a molecule by a DFT software (Gaussian 16) with a standard setting in terms of the basis set and hybrid functional. After that calculation, I viewed the plot about ...
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How can I calculate the exchange energy for a molecule in PySCF?

I am trying to generate exchange energy separately in pyscf but didn't see a way to do that. For correlation energy, it's fairly simple but do you have any idea how to calculate exchange energy?
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Crystallography: How to sample *unique* structures from configuration space? (binary alloy supercell)

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, ...
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List of software for creating random multi-component alloy inputs for DFT or MD

I'm looking for a list of tools similar to ATAT which are available for creating random multi-component alloy inputs for DFT/MD.
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DFT functionals from MP2 methods

I have heard people talk about DFT functionals built starting from MP2 corrections. Do you happen to have a reference I read about that from?
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Bloch wave function extraction for the specific k-points and specific band from QE calculation [closed]

I would like to use QE to obtain u_K(r), which is the Bloch wave function of spin-up maximum valance band at K point. If I define the K point in the input file and do an SCF calculation by QE ...
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Calculating lattice thermal conductivity using Quantum ESPRESSO and phonopy

How should I calculate lattice thermal conductivity in Quantum ESPRESSO? I have installed phonopy. My Linux distribution is Ubuntu.
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1answer
302 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 }(...
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1answer
132 views

HSE06+SOC method using VASP

I have a query on HSE06 + SOC method in VASP. This is a follow-up question to the comment given for a similar question at: How to carry out HSE06+SOC band structure calculation using VASP? I haven't ...
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1answer
141 views

Quantum espresso vs SIESTA

I want to know which particular calculations are suitable for each of them. Is SIESTA free, as in can you work on it without license. (question is based on the fact for now that all these will be done ...
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Is Ubuntu the best option for DFT calculations?

I have just started studying DFT. I did some basic calculations using a Windows system. How will Ubuntu help me if I install it on my system? How much space should I allocate on drive for the Ubuntu ...
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Why does the PBE XC functional not appear to be a sum of exchange and correlation energy?

In the famous 1996 paper of Burke, Perdew and Ernzerhof in the very first paragraph it is stated that $E_{XC} = E_X + E_C$. Then, a GGA functional is derived starting from the energy density of ...
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Quantum confinement of transition metal dichalcogenides (TMDs)

TMDs (transition metal dichalcogenides) are materials that can have a layered structure. When moving from bulk to monolayers, the bandgap changes from indirect to direct according to the image (DFT to ...
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Why is my ORCA calculation of nitrogen iodide failing?

I am using ORCA version 4.2.1 to calculate on the RI-BP86/def2-SVP level of theory the molecule $\ce{NI3}$. I would assume this to be a rather trivial matter, but I am running into an error. I've only ...
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Visualize electron density using pyscf

I found the following example of code which uses density functional theory to compute the electron density $\rho$: ...
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1answer
172 views

External potential in the Hohenberg-Kohn map

I have read the following paper, "Bypassing the Kohn-Sham equations with machine learning", published from Nature Communications in 2017. https://www.nature.com/articles/s41467-017-00839-3 ...
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Is it possible to simulate plasma-material interactions (PMI) using Quantum ESPRESSO? [closed]

I am separately learning about materials modelling using Quantum ESPRESSO (QE), and the theory of plasma-material interactions (PMI). This made me wonder: Is there any way to model PMI using QE even ...
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1answer
49 views

Can a CHGCAR file be converted into a CIF file?

A .cif file can be used for multiple purposes and is a more generic format to store atomic data.
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90 views

How to process electron-density data from a CHGCAR for better handling?

We all know that Vesta helps us visualize the electron clouds present in the CHGCAR data, but I am looking for a better way to process the electron-density data we get in a CHGCAR file for compact ...
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204 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 ...
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The quantum spin Hall 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 ...
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160 views

What is the format of the electron-density data in a CHGCAR file?

Rephrasing the above, what is the pattern in which the electron-density data is stored in the CHGCAR file? I understand that the electron density data in a CHGCAR file is in the form of a 3D Fortran ...
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167 views

Keesom and Debye forces in DFT

Do van der Waals corrected DFT functionals include Keesom and Deby corrections too or just London dispersion? Because when I look at these methods in detail, I see that there is just an attempt to ...
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Calculating emission spectrum of organic compounds by DFT. Can someone elaborate in terms of calculating it for aggregatrion induced emission? [closed]

I am planning for the calculation of emission spectra of organic compounds showing the phenomenon of aggregation-induced emission (AIE). Can someone help me get started?
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Benchmark test cases for DFT program or VASP?

Cross-posted on reddit/comp-chem. I am trying to build my workflow of using DFT to predict properties of some materials, but I am not sure if I do it all right, so I think there might be some ...
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83 views

Why does the S squared value have no meaning in Density Functional Theory?

It is not the first time that I stumble upon the affirmation that spin and the $S^2$ value, under DFT, has no "real physical meaning". Why? If that is true, why are we using it all the time ...
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Creating Interatomic Potential for Lammps using DFT

What are the basic steps and methodologies used in creating inter-atomic potential (specially EAM, MEAM potentials) for metals ...
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269 views

Energy cut-off test meaning in atomic-like basis functions' DFT

I have been using SIESTA code to perform some practicals in my college and I have run energy cut-off tests before calculating properties of semi-conductors or insulator. As far as I am concerned, ...

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