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Results tagged with computational-chemistry
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user 4945
A field which employs computers to model and study chemical systems and chemical behavior, using various models, from approximations of the Schrödinger equation to Monte-Carlo simulations, to modeling with differential equations.
17
votes
When using Gaussian to calculate NMR, what's the default solvent and frequency?
While Greg's answer describes sufficiently what the program does, I would like to extend a little on his remark. (This should have been a comment, but it was too long.)
The HF/STO-3G level of theory i …
- 44.4k
2
votes
How do I calculate the color of a compound?
Since this is quite a broad question, I will also only be able to provide an answer in very broad terms.
The short answer is: You cannot. At least not with (a real) pen and (real) paper.
The slightl …
- 44.4k
3
votes
Accepted
obabel doesn't split molecules
Not knowing which version you are running, it is difficult to actually help you.
I am using Open Babel 2.4.1, and had absolutely no problem separating the two ethylene fragments from the following fi …
- 44.4k
9
votes
3
answers
2k
views
Animate molecular vibrations as multiple xyz coordinate files
I have a frequency calculation by Gaussian09. Now I would like to extract vibrational modes as a set of xyz coordinate files. I would like to manually recompute numerically the points along a transiti …
- 44.4k
3
votes
Accepted
Animate molecular vibrations as multiple xyz coordinate files
As of today I decided to add an answer to this problem to declare it as unresolved. The answer of Klaus only answers the part of visualisation, which is not what I want or need. There are at least ten …
- 44.4k
16
votes
Gaussian: Relaxed scan with modredundant optimization and dummy atoms
Disclaimer: This answer concerns the use of Gaussian 09. While the ModRedundant interface is retained and therefore the same restrictions also apply in newer versions, there is now a newer way of usin …
- 44.4k
4
votes
"No variables in Z-matrix" error in scan calculation of Gaussian
This is a tedious job as a rigid scan as I am unaware of any GUI program that is able to handle a mixed style coordinate input and modification.
DVSA's answer certainly goes into the right direction, …
- 44.4k
8
votes
Gaussian: Relaxed scan with modredundant optimization and dummy atoms
Disclaimer: This answer concerns the use of Gaussian 16. While the ModRedundant interface is retained and therefore the same restrictions also apply to it as mentioned in the other answer. However, th …
- 44.4k
5
votes
Why is CCSD(T)/aug-cc-pVTZ not a suitable method for the geometry optimisation of omeprazole?
Both previous answers by ssavec and jjgoings accurately describe the problem for a single point calculation. Doing a geometry optimisation, you have to run the procedure multiple times until you find …
- 44.4k
5
votes
Accepted
What is the correct approach to obtain PES using CASSCF?
Yes in principle that is a correct approach, but you should be aware of a few pitfalls here and there.
The basis set you chose for your optimisation might not be large enough. I assume you are not go …
- 44.4k
4
votes
How to construct a QST2 input file for Gaussian16 for multiple reactants and products?
TL;DR: QST2 will not work.
For QST2 calculations you need one reactant structure and one product structure, the program will then attempt a transition state guess. The essential point is, that the su …
- 44.4k
5
votes
Accepted
How to calculate the enthalpy of reaction using Gaussian 09?
In principle your approach is correct. There are a few pitfalls though.
Quantum chemistry is usually not well equipped handling ions, especially anions, within reactions, hence the evaluation of the …
- 44.4k
15
votes
Why do post-Hartree-Fock methods fail to predict the direction of the dipole moment of carbo...
The question itself is void, as all methods with the exception of Hartree-Fock predict the direction of the dipole moment correctly. Deathbreath found a Full CI calculation in Jeremy P. Coe, Daniel J. …
- 44.4k
22
votes
1
answer
588
views
How dependent are computed charges using the quantum theory of atoms in molecules on the use...
The quantum theory of atoms in molecules is based on the topology of the electron density. This mathematical analysis allows to find critical points and hence has a unambiguous way of separating a mol …
- 44.4k
17
votes
1
answer
998
views
Why do post-Hartree-Fock methods fail to predict the direction of the dipole moment of carbo...
In carbon monoxide the dipole moment (negative to positive) points towards the oxygen, as I explained it in How can the dipole moment of carbon monoxide be rationalised by molecular orbital theory?
A …
- 44.4k