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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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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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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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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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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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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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 ...
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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}) \...
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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/...
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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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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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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 ...
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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 ...
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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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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, ...
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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 ...
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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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Calculating singlet-triplet gap and open-shell singlet character
I am trying to calculate the singlet-triplet energy gap ($S_0-T_1$) of a conjugated system (18 atoms). For the singlet $S_0$ state, assumed to be closed shell, the Gaussian options were
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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 ...
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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 ...
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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 ...
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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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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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