Questions tagged [configuration-interaction]
Questions to do with configuration interaction theory and applications.
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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^...
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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
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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 ...
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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?
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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 ...
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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 ...
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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 ...
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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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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) + \...
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Start a CI calculation from HF/DFT chkfile in PySCF
I am trying to perform a CISD calculation in PySCF using the starting orbitals from an old DFT result.
The DFT result was saved on a chkfile, mf.hdf5. The code that ...
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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
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Has non-orthogonal CI (NOCI) been implemented in PySCF?
I'm kinda new to Pyscf and was wondering if there is a way to do non-orthogonal CI calculations with it. I would appreciate any help.
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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 ...
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What are the parameters in PySCF's Selected Configuration Interaction code
Dear StackExchange Members,
I'm using the native PySCF implementation of selected configuration interaction (SCI). However, I can't seem to find any documentation detailing the algorithm or various ...
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ORCA: CIS calculation for Helium atom
I want to understand ORCA output for CIS calculations.
From the input file
...
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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.
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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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Core-valence separation (CVS) keyword in MRCC program [closed]
I am interested in using the CVS option in CI calculations to get core-excited states. I tried to use the MRCC program which possesses this option according to the manual (cvs=...). I performed some ...
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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 ...
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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, ...
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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 ...