Questions tagged [multi-reference]

Apply this tag to questions about methods that use multiple determinants to construct the wave function, e.g. MCSCF, MR-PT, CASSCF, MR-CI, etc., questions about chemical systems that might require these methods.

Filter by
Sorted by
Tagged with
3
votes
0answers
36 views

How can I save and read the CI vector during CASSCF calculations in Gaussian?

I have searched through the GAUSSIAN 16 manual and have not been able to solve these two related issues: (1) I want to be able to save the CI vector and load it as an initial guess for a different ...
4
votes
0answers
46 views

What is the theoretical justification for state averaging in SA-CASSCF?

According to the molpro manual, section 7.3: In order to compute excited states it is usually best to optimize the energy average for all states under consideration. This avoids root-flipping ...
9
votes
1answer
525 views

What exactly is meant by 'multi-configurational' and 'multireference'?

Some topics here have touched on this before (see 1, 2, 3), but I haven't found a clear definition yet. I would like to know what exact property of the wave function these terms refer to. It would ...
5
votes
2answers
392 views

The difference between CASSCF and MCSCF methods

I'm not sure the exact difference between the MCSCF and CASSCF methods. I know that the CASSCF method proceeds by optimizing both the CSFs and MOs (I mean the coefficients), but I don't know if this ...
-3
votes
1answer
94 views

How to specify complete active spaces in the Dalton software package? [closed]

What do the numbers for specifying the inactive and active space of a Dalton calculation mean? For example, I do not understand what the following numbers refer to: ...
10
votes
2answers
719 views

How does optimizing the molecular orbital coefficients in CASSCF improve its multi-reference capabilties?

The complete active space self-consistent field (CASSCF) method is a special kind of multi-configurational SCF procedure, attempting to combine Hartree-Fock (HF) and configuration interaction (CI). In ...
6
votes
1answer
372 views

How can I choose the right symmetry in CAS calculation using MOLCAS?

With $C_{2\mathrm{v}}$ symmetry and a closed shell configuration, how can I choose the occupation for each irreducible representation in the input file?
6
votes
1answer
1k views

What are complete active space methods and how are such spaces defined for molecules?

I am new to computational chemistry and would like to know about the active space and inactive space terminologies in MCSCF type calculations. For understanding this I have four systems: $\ce{H2O}$ ...
8
votes
1answer
828 views

Why is no dynamical correlation recovered in the CASSCF method?

Configuration interaction is the only certain way to get a calculation to converge toward the exact solution of the many-body Schrödinger equation (within the approximations used for the framework of ...
7
votes
1answer
973 views

Why is the CASSCF method multi-configurational, while the CI method is not?

The CASSCF method is perhaps the most commonly used theoretical method for studying difficult chemical systems exhibiting multi-reference character or non-dynamical/static/strong correlation. CASSCF ...
5
votes
2answers
127 views

What is a good (small) model system for ligand metal charge transfer practises?

I am looking for an easy to calculate model system in which I could see a ligand metal charge transfer. Basically I am looking for a model complex, that might have the metal/ligand in different ...