Questions tagged [multi-reference]

For questions about electronic structures methods that use excitations from multiple references to model correlation. These are often prefixed with MR (e.g. MR-CC, MR-CI, MR-PT)

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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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9 votes
1 answer
68 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 ...
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7 votes
1 answer
65 views

Frequency error in Gaussian CASSCF(10,10)

I am stuck in calculating the frequencies of one optimised geometry for naphthalene CASSCF(10,10) with Gaussian 16. I have optimised its geometry and checked the active space is the pi system of it, ...
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7 votes
1 answer
64 views

Does PySCF support CAS-SCF calculation?

Does PySCF support CAS-SCF calculations? If not, it is possible to implement it based on their GTO integral library?
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5 votes
1 answer
181 views

Modify ORCA orbitals for CASSCF

I have run a HF calculation on naphthalene and I have checked the MOs that have been obtained. Now, I have to select my active and inactive orbitals for CASCF(10,10). As there are 34 occupied orbitals,...
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6 votes
1 answer
47 views

Multi-configurational self-consistent field coefficients

The total wave function of $H_2$ can be written as a linear combination of configurations built from bonding and anti-bonding orbitals: $${\displaystyle \Psi _{\text{MC}}=C_{1}\Phi _{1}+C_{2}\Phi _{2},...
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11 votes
2 answers
259 views

What are the references in multi-reference methods?

After reading What exactly is meant by 'multi-configurational' and 'multireference'? I still don't understand what the multiple "references" are. I understand that you can for example use a ...
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4 votes
2 answers
87 views

CASSCF and thermochemistry—effect of excited determinants on rotational and vibrational modes

So this question is linked to the other question I asked about the electronic patition function and CASSCF. When calculating thermochemical data (e.g. Gibbs Free energy) the partition functions are ...
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4 votes
1 answer
111 views

Excited determinants, electronic partition function and thermochemistry calculation

While studying statistical thermodynamics I came across the partition functions, which connect the quantum world to the macroscopic world. I understand that partition functions are used to calculate ...
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10 votes
1 answer
188 views

How to determine occupied and closed orbitals for a Molpro CASSCF calculation?

I am currently working with Molpro, to which I am completely new, trying to run some calculations on $\ce{PdO}$. From literature I have gathered that the ground state is given by $^3\Sigma^-$ state, ...
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13 votes
1 answer
175 views

What is a good practical way to determine whether or not I need to use a multiconfigurational method?

I’m planning to run a calculation of single electron transfer where my system goes from singlet to triplet biradical (presumably). So I’m wondering how to decide if I need to use milticonfigurational ...
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12 votes
2 answers
347 views

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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15 votes
0 answers
140 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 ...
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16 votes
3 answers
245 views

What are the types of MCSCF?

Similar to: What are the types of SCF? What are the types of Quantum Monte Carlo? What are the types of ab initio Molecular Dynamics? What are the types of pseudopotentials? What are the types of DFT?...
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9 votes
1 answer
164 views

Can MOLPRO (2012) calculate SA-CASSCF gradients with cc-pVDZ?

I have tried to calculate state-averaged gradients with MOLPRO using the default basis set cc-pvdz. However, I was met with the error message: ...
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