Questions tagged [density-functional-theory]

For questions about simulations using Density Functional Theory.

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41 votes
16 answers
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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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31 votes
6 answers
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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 ...
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27 votes
3 answers
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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 ...
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24 votes
4 answers
702 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 ...
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18 votes
1 answer
1k 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) ...
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24 votes
2 answers
303 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_{\...
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48 votes
5 answers
993 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 ...
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15 votes
2 answers
436 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?
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27 votes
5 answers
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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 ...
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37 votes
1 answer
2k 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,...
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23 votes
3 answers
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What is the appropriate way of determining a value for the Hubbard-like potential U for LDA+U / GGA+U calculations?

It is known that neither LDA or GGA correctly account for the strong on-site Coulomb interaction of localized electrons[1]. A cost-effective way of correcting this is by using a Hubbard-like term $U$. ...
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31 votes
1 answer
790 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 ...
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32 votes
4 answers
6k views

How to write my own density functional theory (DFT) code in Python?

I am a DFT user and at some point in the future, I would like to write my own DFT code in Python to help gain a deeper understanding of DFT. As mentioned in a previous answer people have written their ...
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22 votes
4 answers
1k views

What are the pitfalls for new users of DFT?

This question is inspired from a post in another SE. Many users these days use density functional theory codes as 'black boxes' and hence its natural to expect that they would have made many mistakes ...
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24 votes
3 answers
2k views

What does B3LYP do well? What does it do badly?

I have seen a general criticism of B3LYP in computational chemistry (especially with the 6-31G* basis set). I would like to know some of the more/less obvious problems that occur when using it and ...
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18 votes
3 answers
2k views

k-points and ENCUT convergence tests before or after relaxation?

Let's say I want to relax a structure using VASP. K-points and ENCUT convergence tests must be conducted before or after relaxation? and which tags should be ...
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38 votes
5 answers
1k 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 ...
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32 votes
3 answers
798 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, ...
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17 votes
1 answer
368 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 ...
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16 votes
2 answers
343 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 ...
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15 votes
1 answer
864 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 ...
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20 votes
3 answers
500 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 ...
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11 votes
5 answers
565 views

Create doped structures to POSCAR files for vasp

I have a perfect supercell structure Ni fcc. And I would like to dope another element O or N with a ratio of O:Ni=8:100 to the supercell of 3x3x3 and find the most stable ordering structure. The ...
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13 votes
2 answers
303 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 ...
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10 votes
2 answers
254 views

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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19 votes
3 answers
859 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.
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17 votes
2 answers
1k 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.
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25 votes
1 answer
666 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. ...
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16 votes
3 answers
457 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 ...
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16 votes
2 answers
2k views

How to explain to a five year old why "DFT with local exchange–correlation functionals do(es) not describe van der Waals interactions accurately"?

From How do you explain Canada's Trudeau's power-sharing agreement to a five-year-old (American)?: The "explain to a five-year-old" question is a semi-standard format where the answer ...
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15 votes
1 answer
280 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 ...
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13 votes
2 answers
413 views

What are good resources to learn Materials Modeling?

I wonder if there are any books or resources to start learning Materials modelling using methods density functional theory quantum monte carlo molecular dynamics
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26 votes
3 answers
617 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 ...
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15 votes
2 answers
1k views

Total spin and/or multiplicity for transition metal ions?

I am trying to input various charge states of various transition metal ion species into DFT calculations. The program requires an input of multiplicity = 2*(total spin) + 1. I have an undergraduate-...
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12 votes
2 answers
3k views

What is the difference between DOS and PDOS?

I'm new to DFT. Can you please help me to understand DOS and PDOS (projected density of states) in simple wording? I only want to know some basics of these terms and how they are linked to DFT.
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9 votes
1 answer
3k views

What is the physical meaning of occupations='smearing' in Quantum ESPRESSO?

I want to understand, what is the intuition behind using the occupations='smearing' or 'tetrahedra' in Quantum ESPRESSO input file? I mean how we can interpret what is going to happen inside of ...
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17 votes
3 answers
502 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 $...
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  • 919
15 votes
5 answers
588 views

What are some open-source all-electron DFT alternatives to Wien2K?

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 ...
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13 votes
1 answer
2k views

Monkhorst-Pack, Gamma-centred and gamma only

Sorry if this question is too simple for this community but I still couldn't find an answer to it. Do gamma-centred and gamma only grid mean the same thing? If not, what's the difference? How do they ...
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13 votes
2 answers
549 views

How to convert Unified Pseudopotential Format (UPF) into Ultrasoft Pseudopotential (USPP) format?

I am working on DFT code having plane wave along xy axis and bspline in z direction. For calculating the properties of TMD materials, spin orbit coupling must be included but i did not find fully ...
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12 votes
1 answer
231 views

What is the best program to manipulate numerical DFT wavefunctions to calculate custom matrix elements?

For pedagogical reasons, I am looking for ways to calculate quantum-mechanical quantities such as $\langle m | \dot{m}\rangle, \langle m | \dot{n}\rangle, \langle m | \ddot{n}\rangle$ using ...
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9 votes
1 answer
1k views

How to carry out HSE06+SOC band structure calculation using VASP?

I could not find any good source for this type of calculation. I'd be very appreciated if someone who is experienced with that to show it step by step
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  • 1,011
8 votes
1 answer
234 views

How to evaluate the electron relaxation time of nanostructures computationally

I am working with Si nanowires using the SIESTA ab initio code and the BoltzTraP2 Boltzmann transport equation solver. However, the output of the BoltzTraP2 code comes per relaxation time (...
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  • 2,526
5 votes
1 answer
171 views

Different between ENCUT and ENAUG in the VASP setting?

I am trying to figure out the difference between ENCUT and ENAUG in VASP settings, I found the following description on the wiki of VASP. ENAUG specifies the cut-off energy of the plane wave ...
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  • 1,681
18 votes
3 answers
329 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 ...
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17 votes
1 answer
714 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 ...
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14 votes
3 answers
611 views

Determining Fermi energy in density functional theory

Fermi energy is affected by the temperature and whether the material is an insulator/semiconductor/metal, but how is the Fermi energy determined in DFT calculations and how reliable are the obtained ...
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13 votes
2 answers
552 views

Which property should be used for a DFT convergence test? Is energy always the best, or should convergence be tested for a different property?

As I pointed out in the other question Convergence test I: same atoms and different structures, each time you start a DFT calculation you need to do a convergence test. Normally, we use the system ...
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  • 19k
11 votes
1 answer
1k views

How to model an anti-ferromagnetic crystal in quantum ESPRESSO properly?

I'm fairly new to DFT. I would like to plot the DOS and band structure of Cobalt Oxide (CoO). But since CoO is anti ferro magnetic, how would I approach the problem? would I create an input file ...
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10 votes
1 answer
600 views

Spin–orbit interaction with DFT

I'm new to DFT. Does the DFT take into account the spin-orbit interaction? On the one hand, this is a relativistic effect, perhaps DFT does not take it into account. However, on the other hand, I ...
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