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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Is the electron-electron interaction to blame, for the added complexity of using "orbitals" for an N-electron system?
In a one-electron system such as the H atom, we are able to say that the orbitals are valid wavefunctions. But for complex systems with N-electrons, I have heard people say that they are just ...
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Is the one-electron reduced density matrix enough in DFT?
There is a conceptual mismatch in my personal understanding between the role of reduced density matrices in DFT and post-HF methods (possibly due to different discussions in textbooks), and I can not ...
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Why is electron correlation called the "chemical glue"?
A significant part of quantum chemistry involves developing methods that go beyond the Hartree-Fock theory which treats electron-electron interactions through a mean-field approach. From what I ...
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Strongly Correlated Materials: Theoretical Frameworks, Computational Techniques, and Machine Learning Breakthroughs in Matter Modeling
This is more of an opened discussion, recommendations, and experts views on the Strongly correlated materials.
Exploring the behavior of strongly correlated materials poses significant challenges in ...
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To what extent can coarse-grained models retain the essential quantum mechanical characteristics of a system?
To what extent can current coarse-grained models, within the context of multiscale modelling, retain essential quantum mechanical characteristics such as electron correlation, polarization, and ...
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How is the LUMO lower energy than the HOMO for triplet state restricted-open shell DFT calculation?
I recently ran a calculation using the ROB3LYP/LANL2DZ level of theory for a triplet spin molecule. While analyzing the results, the HOMO is doubly degenerate and the LUMO is singly degenerate. I ...
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What is the physical meaning of the term "non-local interaction"?
This term pops up through out Hartree-Fock and DFT. Does this term have any physical significance to actual(real) system or it is a mathematical by-product?
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Hubbard U value on LaAlO3/SrTiO3 interface [closed]
I want to do a GGA+U calculation on the LaAlO3/SrTiO3 heterostructure to study the 2DEG formed at the interface. In all the references I came across they used U around 4eV-6eV on Ti 3d orbitals, I'm ...
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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 ...
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Are frozen-core approximations for the elements of first or second row accurate for potentially extremely short bond distances present in the molecule
Yes, it is about my molecule that you've heard of (but never seen) in my previous questions. The molecule, which contains only C, Al, B, Cl, Mg, N, O, S and Si, is macromolecular with quite crowded ...
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Are multiplet free atoms multireference?
In general, my understanding is that free radicals and non-equilibrium molecules sometimes need multireference electronic structure calculations, mainly because of different electronic states being ...
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Is there any relation between static correlation and finite-temperature smearing?
I am new to this field, so there is a chance that I am mixing two entirely different concepts together, but it seems to be that static correlation and finite-temperature smearing in DFT are somehow ...
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Convert ase atoms to pymatgen structure
I have atom_row from ase_db.
I have tried various methods but they all fail. Seems like I'm missing a lattice, but I don't know what that is and where I can get it ...
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What correlation effects are included in KS-DFT with LDA and GGA?
This post is inspired by this post: What correlation effects are included in DFT?
The Kohn-Sham density functional theory (KS-DFT) are considered to be exact and can include all correlation effects in ...
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Why are Norm-conserving Pseudopotentials considered so important?
So I am aware that a norm-conserving pseudopotential enforces the conditions that:
Inside the cut-off radius, the norm of each pseudo-wavefunction is identical to its corresponding all-electron ...
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Is it possible to make segmented contracted basis sets for correlated calculations?
The segmented contracted basis sets are usually handled well by the QM programs than generally contracted basis sets, as the primitives are not repeated. The correlation consistent basis sets (cc-PVnZ)...
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For which materials is the Bethe lattice a good model to compute the density of states of the conduction band? [closed]
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....
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What is static correlation, actually?
My question is inspired by this question and also this one. I have come across the term static correlation multiple times. Introduction to Computational Chemistry by Frank Jensen describes static (or ...
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How does static correlation differ from Fermi correlation, and how does dynamic correlation differ from Coulomb correlation?
From what I read, the correlation energy can be grouped as static correlation and dynamic correlation. Another way to group them is Fermi correlation and Coulomb correlation.
Is there any link between ...
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When do we abandon ab initio methods?
This question is related to (and was originally asked in) another post about "quantum protectorates" I made here.
Ab initio methods are nice because they directly solve a sort of "...
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How should I compare different basis sets for post-Hartree-Fock methods?
HF or DFT methods are variational so I can confidently say that any basis set that gives the lowest energy is the best for that system. However, I have learnt that post-HF methods such as MP2, MP3, ...
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What are Pair Natural Orbitals?
Recently, I came across electron correlation methods that use local pair natural orbitals (LPNOs) or domain-based local pair natural orbitals (DLPNO), such as DLPNO-MP2, DLPNO-CCSD etc. The dynamic ...
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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 ...
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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 ...
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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,
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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 ...
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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 ...
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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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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 ...
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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, ...
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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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