Questions tagged [configuration-interaction]
Questions to do with configuration interaction theory and applications.
17
questions
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Why is my CISD restart failing in PySCF?
A case that works
In my answer to Restarting an FCI calculation in PySCF, I provided a folder full of input and output files that demonstrates saving (as a numpy ...
- 30.9k
3
votes
1
answer
71
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Is PySCF able to print checkpoint files during a CISD calculation?
The problem
I've described how to restart a CISD calculation in my answer to the question: Restarting an FCI calculation in PySCF, but this requires all iterations of the CISD calculation to finish, ...
- 30.9k
4
votes
2
answers
235
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Which properties would you study to evaluate spatial confinement of a molecule
I'm modelling molecules confined within porous materials and I was wondering which molecular properties would you consider to access the confinement.
Í'm thinking about looking into long-range ...
- 343
5
votes
1
answer
57
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Finding the Configuration State Functions of Atoms
Is there a book or tabulated work where the configuration state functions of atoms have been documented? Just as useful would be information about computer programs that are able to predict the CSFs.
- 346
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1
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158
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ORCA: CIS calculation for Helium atom
I want to understand ORCA output for CIS calculations.
From the input file
...
- 357
11
votes
2
answers
330
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FCI without Hartree-Fock
Recently, I came across some lecture notes on electronic structure theory which had something peculiar about it. I noticed that FCI (configuration interaction) was introduced before Hartree-Fock ...
user784
6
votes
1
answer
119
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Transforming from CI basis to MO basis
Suppose, one knows the ground state wave function $|\Phi\rangle$ in terms of a slater determinant(SD) basis say, from a Configuration interaction calculation.
$$|\Phi\rangle= c_{\text{HF}}\left|\Psi_{\...
user784
8
votes
1
answer
533
views
What do size-extensivity and size-consistency mean?
I have heard both terms in various lectures and books on quantum chemistry, however, I have not found a proper explanation of them. As I understand now, size consistency of a method means for example, ...
- 6,216
9
votes
1
answer
91
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Which molecules have multi-reference character?
I'm using WebMO to construct molecules that have high multireference character, but I cannot seem to find any, or perhaps I'm not building them correctly on WebMO; I know singlet biradicals generally ...
6
votes
1
answer
78
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Accurate electron-hole localization for charge-transfer transitions
I'm studying the nature of electronic excitation in conjugated organic dyes.
To define the donor and acceptor part I've run TDDFT and CIS calculation, they both gave similar set of configurations for ...
- 2,333
11
votes
3
answers
496
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CCSD and CISD size-consistency problem
I have performed a Gaussian16 calculation to explore the size-consistency problem for the CISD method. The system I am studying is the water dimer and the results are not what I expected at first. I ...
- 957
8
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106
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How to classify ionic and covalent excited-states? [closed]
In spectroscopy it is common to describe excited-states as ionic or covalent.
I understand the concept on a toy model e.g. $\ce{H2}$ with a minimal basis set
\begin{align}
\Phi_0 &= [\chi_A(1) + \...
- 7,869
9
votes
1
answer
265
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PySCF: eigenvalues, non-integer occupation, CISD calculations, and frozen lists
I have been performing CISD calculations with PySCF and I have a query surrounding the occupation of the orbitals. Here, the occupancies are calculated from the eigenvalues of the 1-electron ...
- 1,869
5
votes
1
answer
166
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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,
...
- 1,603
9
votes
1
answer
63
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Extended Hybrid Methods
Hybrid DFT methods, where the functional is supplemented with Hartree-Fock exchange, have become increasingly popular due to their low cost and decent accuracy. Double hybrids, which mix in an MP2 ...
- 14.5k
10
votes
1
answer
82
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Are there any programs that can do non-orthogonal CI?
Could you list any programs that can do non-orthogonal CI please?
- 1,335
25
votes
2
answers
338
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How to overcome the exponential wall encountered in full configurational interaction methods?
Similar to how a molecular orbital, also known as a 1-electron wavefunction, can be represented with a linear combination of “basis” functions, e.g., atomic orbitals (LCAO):
$$\Phi(\mathbf{r})=\sum_i^...
- 7,869