Questions tagged [electron-correlation]

Questions relating to electron correlation - the interaction between electrons in the electronic structure of a quantum system. The correlation energy is a measure of how much the movement of one electron is influenced by the presence of all other electrons.

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9
votes
2answers
57 views

Quantifying electronic overlap?

I am trying to understand how to quantify the electronic interaction/conduction/overlap between two metal cores at varying distances. As someone who works primarily with classical MD, and has less ...
7
votes
1answer
59 views

What are the methods for calculating interaction energies of layered materials, and where are they implemented?

What are the available methods for the calculation of reference interaction energies of layered materials and in which codes they are implemented? For example, I know RPA-ACFDT in the DFT concept. But ...
5
votes
1answer
86 views

What are the other matrix elements in singlet symmetry-adapted CISD?

Szabo/Ostlund list the CI matrix elements between singlet symmetry-adapted configurations (SAC) in Table 4.1 of their book: $$ \langle ^1\Psi^r_ a \lvert \mathcal{H} - E_ 0 \rvert ^1\Psi^r_ a \rangle, ...
6
votes
0answers
24 views

For which materials is the Bethe lattice a good model to compute the density of states of the conduction band?

The Bethe lattice is exactly solvable in the limit where each lattice site has an infinite number of nearest-neighbors. In this limit it yields a semi-circular density of states in the conduction band....
8
votes
0answers
40 views

What are the ways to add dynamic correlation to an MCSCF wavefunction?

We recently learned about the many types of MCSCF, which treat "static" electron correlation. There are then many ways to treat further "dynamic" electron correlation to try and ...
11
votes
1answer
62 views

What are the practical limitations of R12/F12 methods?

Electron correlation methods based on an expansion of the $N$-electron wavefunction in terms of Slater determinants have a slow basis set convergence. Moreover, explicitly correlated methods (such as ...
12
votes
3answers
93 views

Physically motivated double hybrid DFT?

This question came to mind while writing another question here Extended Hybrid Methods, but I felt it was distinct enough to ask separately. In double hybrids DFT methods, you essentially perform a ...
11
votes
2answers
89 views

What are the computational limits of explicitly correlated methods?

Expanding the $N$-electron wavefunction in terms of Slater determinants (as in CI and CC theory) could lead to a very slow convergence to its basis set limit because such expansions can't give an ...
22
votes
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 ...
22
votes
2answers
128 views

How to determine, a priori, whether a compound has multireference character?

We say a system has multireference character if it is not well described at the SCF level by a single configuration/Slater determinant. Not accounting for this can lead to errors in post-SCF methods, ...
29
votes
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 ...