All Questions
Tagged with multi-reference computational-chemistry
13 questions
1
vote
0
answers
30
views
Charge Transfer and Multireference Methods
I have read in literature that systems that exhibit "high charge-transfer character" are best treated using multireference/multiconfigurational methods. Why is that? What makes such a system ...
- 11
1
vote
0
answers
30
views
How can I understand if my system has degenerate electronic configuration?
How can I understand if my system has degenerate electronic configuration?
I'm running some post-HF methods and in the meanwhile try to understand which is the most accurate method for my system. ...
- 11
2
votes
0
answers
99
views
What are the references in multi-reference methods? [closed]
There is this question: What exactly is meant by 'multi-configurational' and 'multireference'?
But I still don't understand what the multiple "references" are. I understand ...
- 121
4
votes
0
answers
158
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 ...
- 1,026
5
votes
0
answers
447
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 ...
- 1,026
24
votes
2
answers
8k
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 ...
- 1,459
9
votes
2
answers
2k
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 ...
- 183
-2
votes
1
answer
275
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:
...
- 353
6
votes
1
answer
857
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?
- 109
9
votes
1
answer
4k
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:
$\ce{H2O}$
...
- 1,582
10
votes
1
answer
2k
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 ...
- 4,773
7
votes
1
answer
2k
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 ...
- 4,773
7
votes
2
answers
171
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 ...
- 44.4k