Questions tagged [configuration-interaction]

Questions to do with configuration interaction theory and applications.

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1 answer
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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.
5 votes
1 answer
75 views

ORCA: CIS calculation for Helium atom

I want to understand ORCA output for CIS calculations. From the input file ...
  • 357
11 votes
2 answers
312 views

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 ...
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6 votes
1 answer
115 views

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_{\...
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8 votes
1 answer
350 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, ...
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9 votes
1 answer
77 views

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
75 views

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 ...
  • 2,323
11 votes
3 answers
392 views

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 ...
8 votes
0 answers
103 views

How to classify ionic and covalent excited-states?

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) + \...
  • 7,794
9 votes
1 answer
217 views

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 ...
  • 1,829
5 votes
1 answer
138 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, ...
  • 1,603
9 votes
1 answer
58 views

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 ...
  • 14.3k
10 votes
1 answer
78 views

Are there any programs that can do non-orthogonal CI?

Could you list any programs that can do non-orthogonal CI please?
25 votes
2 answers
307 views

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^...
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