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Questions tagged [density-functional-theory]

Density functional theory (DFT) is a quantum mechanical model used to estimate the electronic structure of molecules and condensed matter. In broad terms, DFT works by treating all the electrons in the system as a single electron density, and computing physical quantities of interest as functionals of that electron density. (from Physics.SE)

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29
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4answers
3k views

DFT Functional Selection Criteria

I have a very very general question: In DFT functional selection , mostly people speak about the most recent ones. For example my professor always asks: " which DFT Functional did you select ? " ...
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Striking examples where Kohn-Sham orbitals clearly have no physical meaning

In Density Functional Theory courses, one is often reminded that Kohn-Sham orbitals are often said to bear no any physical meaning. They only represent a noninteracting reference system which has the ...
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1answer
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What's the difference between PBE and B3LYP methods?

I can't find an answer to that question. I was told that in B3LYP, more variables implemented in the method are empirical, but I can't find anywhere if it's true, and I'm sure it's not the only ...
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998 views

Equivalent of Szabo and Ostlund book for DFT

Szabo and Ostlund book Modern quantum chemistry [1] is extremely useful to understand Hartree-Fock and post-Hartree-Fock methods. Not only it explains the theory behind such methods, but it is also ...
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2answers
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Is density functional theory an ab initio method?

The following comment by Wildcat made me think about whether density functional theory (DFT) can be considered an ab initio method. @Martin-マーチン, this is sort of nitpicking, but DFT (where the last ...
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3answers
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Are there any full worked examples of DFT calculations?

I just started learning DFT and now I am totally confused. Assuming I want to use B3LYP: \begin{align} v_s\left(\textbf{r}\right) &= v_\text{ext}\left(\textbf{r}\right) + \int d^3r\frac{n\left( \...
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2answers
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Why are correlation consistent basis sets used with DFT calculations?

Reading some papers, there is a bit of a curious observation that does not exactly make a lot of sense to me. In Quantum Chemistry, different methods exist to carry out geometry optimisation and ...
10
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1answer
201 views

How does one actually get the energy from the Kohn–Sham equations?

This might be a silly question, but how does one acquire the energy of the system from the Kohn–Sham equations? $\left[ -\frac{1}{2}\nabla^2 + V_{eN}(\vec{r}) + V_{ee}(\vec{r}) + V_{xc}(\vec{r}) \...
27
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1answer
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Suggest methods and basis sets for a variety of systems

Please help me with any/all of the cases below. In the following cases, the named method and basis set are not suitable for the chemical systems. Why aren't they? Could you suggest a suitable method/...
13
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2answers
1k views

What do short-range and long-range corrections mean in DFT methods?

Currently I am looking for the most accurate calculation method for a simple non-conjugate molecule consist of C, N, O and H. Normally I would try each method for a similar and known molecule then ...
11
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4answers
599 views

Defining and testing custom made DFT functionals?

What is a good and free software for this endeavor? Any recommended articles on the subject? I want to design dft functionals, trying out different parametrizations and optimizing mixing constants for ...
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3answers
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Exchange-correlation hole

I did a google and chemistry.exchange search and found several technical definitions of the exchange correlation hole. The questions that I want to proposes are: What the exchange-correlation hole ...
15
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1answer
4k views

Interpretation of TD-DFT results

For the first time I'm doing TD-DFT calculations (wB97XD functional) in Gaussian 09 for an open-shell system and the results look like the hell of a mess for me. The molecule is rather big, so I ...
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Density Functional Definition

Is it wrong to say that Density Functional means that Electron Density is a function of the orbitals (wave function) of all electrons in 3 dimensions, if so, why ?
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3answers
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PBE vs. PBEPBE functional

I've found good explanation what the PBE functional is. However, sometimes I see PBEPBE and I cannot find any good information about what this means and how it's different from PBE. The Gaussian ...
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1answer
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Calculating dipole moments from atomic partial charges

How can I calculate dipole moment of a complex molecule where the partial charges are available from density functional theory? I have the coordinates of each atom from atomistic simulations of an ...
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2answers
188 views

Geometry optimization: dependence on initial geometry

One would think that initial configuration should not significantly impact the final optimized geometry. Starting with two moieties, the final "optimized" geometry is not unique and depends highly on ...
4
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1answer
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Finding mathematically the ground state density in DFT

To find the ground state density in DFT, you set the following Lagrangian: $$L = E[\rho(\vec r)] - \mu\left(\int \rho(\vec r) \mathrm{d}\vec r - N\right)$$ While minimising with respect to the ...
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0answers
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DFT Exchange-Correlation Two Electron Integrals

Are there any electronic structure programs that print the exchange-correlation (XC) integrals for a given DFT functional? These integrals are of the form $$\langle pq|w|rs\rangle$$ where $w$ is an XC ...
11
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1answer
158 views

Estimating stability and mean life of anomalous tautomers

A pair of bases in the DNA, say, A-T, have a tautomerized form A*-T* (resulting from switching the sides of both protons along the hydrogen bridges). I have studied how, by means of DFT computations, ...
8
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1answer
967 views

Difference between single point energy and dimerization energy

I am investigating potential energy surface characteristics of some electrostatic monomeric interactions e.g. $\ce{F-H}$...$\ce{F-H}$. I'm using DFT and SCS-MP2 to perform the necessary calculations ...
4
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1answer
96 views

Correlation energy in quantum chemistry

In density functional theory (DFT) there is classic Coulomb energy and non-classic correlation energy. But what is difference between them? In books these energies are explained very similarly. Both ...
4
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1answer
977 views

Is there a relation between transition density and density differences?

When I have an excited state, is there a relation between the transition density associated with this electronic transition and the density difference between the excited state density and the ground ...