Questions tagged [density-functional-theory]

For questions about simulations using Density Functional Theory.

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36
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13answers
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What are some recent developments in density functional theory?

In the book Materials Modelling Using Density Functional Theory: Properties and Predictions by Feliciano Giustino, a timeline of milestones in DFT was given for achievements between 1964 and 1996: $$\...
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5answers
1k views

What are the types of DFT?

Similar to: What are the types of charge analysis?, What are the types of bond orders?, and What are some recent developments in density functional theory?, I would like to ask: What are the different ...
15
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1answer
188 views

Are there differences in accuracy and reliability between the frozen phonon method and Density Functional Perturbation Theory?

When proposing or predicting new materials, whether in the bulk or in two dimensions, it is important to discuss the stability of the system. This is usually done through thermodynamics and(or) ...
14
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2answers
155 views

What are the types of pseudopotentials?

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?
39
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4answers
449 views

What is the closest thing we have to “the” universal density functional?

It is understood that finding "the" universal functional is an NP-complete problem. However, progressively better functionals have been constructed decade after decade and fitted to more and more ...
32
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5answers
566 views

Why do we have so many DFT codes (softwares)? Are they redundant?

Lejaeghere et. al studied reproducibility of DFT codes (softwares) by comparing 15 different codes employing 40 different potentials. The study concluded that most codes agree very well, with ...
24
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2answers
199 views

What are the positives and negatives of periodic DFT codes that don't use plane-wave basis sets?

Most periodic density functional theory (DFT) codes use plane-wave basis sets in conjunction with three-dimensional periodic boundary conditions. In contrast, for molecular systems of finite size, ...
22
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2answers
218 views

What are the different ways of calculating dispersion constants?

There are many different dispersion corrections out there. The most famous is D3 [1] (and the new D4 [2]), but there's probably other approaches too. The dispersion energy can be written as: $$ E_{\...
18
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3answers
261 views

Are there any online course/video lectures available on Density functional theory?

Please mention good online video lectures on theoretical foundations and practical implementation of DFT.
32
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1answer
1k views

Was Walter Kohn wrong about this?

In Kohn's Nobel Lecture, he claimed that: "In general the many-electron wave function $\Psi(\mathbf{r}_1,\ldots,\mathbf{r}_N)$ for a system of $N$ electrons is not a legitimate scientific concept,...
29
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1answer
187 views

What correlation effects are included in DFT?

In wavefunction methods the accuracy of the description of a system of electrons can be improved systematically starting from a reference, usually a Hartree-Fock wavefunction. This difference between ...
15
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2answers
99 views

In DFT, if I complete a convergence test once, then want to study a different system with the same atoms, do I have to do a new convergence test?

Any time you start a new DFT calculation, it is recommended to do a convergence test. The parameters to include in the tests vary depending on the DFT implementation, i.e. plane-waves, Gaussian basis ...
22
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5answers
351 views

When and Why does Density Functional Theory (DFT) fail?

Every method has its strengths and weaknesses. For instance, a strength of DFT is that is has HF like speeds, but can also account for electron-correlation and this is a pretty big feature since ...
17
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3answers
210 views

What are the core numerical routines used in density functional theory?

It looks to me to that many of the things one would do within the framework of density functional theory (DFT) ultimately boil down to solving a generalized eigenvalue problem $Av = \lambda Bv$ where $...
23
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3answers
243 views

What is the largest material that has been studied using density functional theory?

Quantum-chemical calculations are quite expensive with a cost that scales greatly with the number of atoms in the system. What is the largest material that has been modeled using density functional ...
12
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2answers
175 views

What are the scientific justifications of the binding energy equation?

There are many problems where we want to calculate the binding energy between two systems. Normally, we have a system A, adsorbent (a surface, a nanotube, a protein, etc.), that interact with a system ...
22
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4answers
186 views

Available methods and codes for materials discovery / crystal structure prediction?

There are many open databases and projects that allow you to access computed crystal structures of experimentally known compounds, registered in the Inorganic Crystal Structure Database (ICSD). These ...
16
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1answer
88 views

How to evaluate spin exchange parameters of a magnetic material using DFT?

I think we have to calculate total energies using different FM, AFM configurations and solve a set of linear equations. How to arrive at the set of equations for any given structure? An example from ...
20
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4answers
257 views

Difficult cases for converging Kohn-Sham SCF calculations

In a recent article by Woods et. al.[1] a couple of methods for converging ground-state Kohn-Sham DFT calculations are reviewed and compared. In their test suite they give plenty of examples for badly ...
18
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1answer
330 views

Mathematical expression of SCAN (Strongly Constrained and Appropriately Normed) constraints in DFT

(This question is originally posted on physics stackexchange, but someone suggested me to post on this site, so there you go) I'm compiling the mathematical expression of SCAN (Strongly Constrained ...
16
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3answers
823 views

I am a beginner in DFT. What are some resources that could help me to learn the basics?

I am a beginner in DFT. Please suggest me some good material to understand the basics.
15
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1answer
131 views

What are the pre/post processing tools available for VASP?

I am aware of pyPROCAR and VASPKIT. Are there any other tools supporting VASP
15
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3answers
197 views

How to calculate homolytic bond dissociation energies?

An experimental colleague asked me how hard it would be to calculate homolytic bond-dissociation energies for different phosphonates which are involved in a Hydrophosphination. The compounds include ...
20
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3answers
876 views

Given that Kohn-Sham DFT is strictly a ground-state method (at 0 K), how is it sufficient to describe materials in real-life applications?

Kohn-Sham DFT appears to be so popular even though it is strictly a ground-state method - all calculations are done at 0 K. How then, is it so popular when describing materials that have real-life ...
19
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2answers
117 views

Norm-Conserving or Ultrasoft, which pseudopotential to choose?

Ultrasoft pseudopotential (USPP), in general, requires a lower energy-cutoff to the plane waves when compared to Norm-Conserving ones (NC). On the other hand (at least with Quantum ESPRESSO) the ...
19
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2answers
1k views

How to “get my feet wet” in Density Functional Theory by simulating a water molecule using Python

I just saw I am a beginner in Density Functional Theory. What are some resources that could help me to learn the basics? and it reminded me that few years ago I'd asked How can I calculate the charge ...
16
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1answer
147 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 ...
13
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2answers
209 views

How to calculate energy of a molecule in an aligned electric field?

So I am aware that many quantum chemical codes are able to add external fields to molecular calculations (for example to calculate polarizabilities). I also know that in some (eg. Orca) you have some ...
12
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1answer
157 views

Great computer graphics for matter modelling

I am trying to write some code to automatically generate a judicious set of graphics from DFT/fn-DMC calculations so that users can sanity check their results quickly. My literature review has found ...
11
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1answer
194 views

What are good resources to learn Materials Modeling? [closed]

I wonder if there are any books or resources to start learning Materials modelling using methods density functional theory quantum monte carlo molecular dynamics
25
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2answers
198 views

What are the best functionals for transition metal compounds?

Some properties of transition metal compounds can be influenced by static correlation, relativistic effects, and, in some cases, close-lying electronic states could result in difficulties in SCF ...
22
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1answer
154 views

What are good ways to reduce computing time when working with large systems in VASP?

I know that parallelization is an important factor, however, I wanted to know if there are any other methods of reducing computing time when dealing with large systems without sacrificing accuracy. ...
18
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3answers
237 views

How to do periodic DFT calculations using Quantum ESPRESSO?

I have only done quantum mechanical computations using non-periodic wavefunctions. I'd like to try to periodic-wavefunction density functional theory. Quantum ESPRESSO seems like a good package ...
18
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2answers
130 views

Calculating binding energy between two systems

Regarding the calculation of binding energy of molecular absorption on graphene, for which this has been discussed before, the process of calculating $E_{AB}$ is fairly straight forward, i.e., it is ...
17
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2answers
113 views

Is there any relevant DFT formalism apart from the Kohn-Sham approach?

I wonder if all DFT codes are based on the Kohn-Sham formalism?. If other methods are available, what are their scopes?
16
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1answer
182 views

The Hund's J - Why can this be quantified?

I was reading on the implementation of Hubbard 'U' in Density Functional Theory. The Hubbard 'U' can be thought of as a parameter that accounts for the on-site electron-electron interactions in ...
16
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1answer
125 views

Exchange-Correlation Two-Electron Integrals

Do any freely available or proprietary electronic structure packages explicitly compute two-electron exchange correlation integrals? I have found a few derivations to calculate excited state ...
14
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1answer
306 views

Difference between Van der Waals (DFT-D and DFT-D3) corrections in ab-initio calculations

In Kohn-Sham DFT calculations, Van der Waals corrections are often implemented in the structure optimization calculations because the typical functionals such as LDA and GGA are found to not treat ...
12
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1answer
232 views

Can DFT be 'exact' in the limit of the uniform electron gas?

I was wondering if DFT (or specifically, LDA ?) can be exact in the limit of the homogeneous electron gas? In that case, shouldn't the self-interaction error perfectly cancel out? I realise that such ...
9
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2answers
153 views

Methods for studying superconductivity?

From Wikipedia, superconductivity is the set of physical properties observed in certain materials where electrical resistance vanishes and magnetic flux fields are expelled from the material. Any ...
7
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1answer
36 views

Work Function Problem

2D materials (such as graphene) are mostly exfoliated from their 3D bulk counterpart. I am wondering how we can calculate work function for a 2D material? Normally electrostatic potential in the out-...
17
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3answers
125 views

How trustworthy is the Tran-Blaha modified Becke-Johnson potential and how does it perform across basis sets?

When modeling solid-state materials and particularly semiconductors, one must go beyond LDA and GGA. One alternative is to use hybrid functionals or the $GW$ method. However, this can be very ...
17
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1answer
139 views

What are some approaches to modeling charged point defects in materials?

From what I understand, one major issue in modeling charged point defects in materials is the existence of artificial interactions between charged defects and their periodic images. Even when using ...
17
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1answer
210 views

Are there problems with the Tran-Blaha modified Becke-Johnson potential (mBJ, a.k.a. TB09) in Quantum ESPRESSO?

I have used the modified Becke-Johnson (mBJ) exchange potential before, as it was developed and implemented in Wien2K by Fabien Tran and Peter Blaha (1). In 2013, Éric Germaneau et al. implemented mBJ ...
16
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2answers
194 views

Is the electronic band gap the only thing that is affected, when switching from standard KS-DFT to Hybrid functionals?

It is very well known that Kohn-Sham DFT underestimates bandgap. To get an accurate estimate of the bandgap, people often turn to Hybrid functionals (if they don't want to perform the actual ...
14
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1answer
161 views

Standard values for level of convergence

In matter modelling we use self consistent approaches for calculating different properties. Many DFT codes find the ground state of the system by determining total energy self consistently. Going ...
14
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2answers
93 views

Appropriate functionals for prediction of NMR spectra of transition metal compounds

In line with this question, I'm looking for suitable functionals for transition metal compounds with organic ligands to predict NMR spectra. Also, I'd like some guidelines about how to choose ...
12
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1answer
106 views

Justification for use of Screened Functionals

Hybrid density functionals with screened Hartree-Fock exchange at long range have become popular for modeling solids. I'm curious as to what the reasoning is behind this functional form. I understand ...
12
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1answer
107 views

Why is the Nonequilibrium Green’s function (NEGF) method for quantum transport not implemented in plane wave codes like VASP and Quantum Espresso?

DFT codes like Siesta, QuantumATK, Questaal, and Smeagol having localized basis sets have NEGF implementations available. But not in plane wave codes like VASP and Quantum Espresso. Why is it so?
11
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2answers
124 views

Which properties of a material calculated using density functional theory are affected by smearing?

Smearing (smearing width $\sigma$, to be precise) has always been confusing. I understand what it is but can't pin it down when it comes to DFT calculations. Should it be converged like k-points and ...