Chemistry Spectra of small molecule and computed spectra

  • Thread starter Thread starter greisen
  • Start date Start date
  • Tags Tags
    Molecule Spectra
AI Thread Summary
Calculating the spectra of a small molecule, specifically benzene with a nitrogen group, reveals significant discrepancies between DFT B3LYP results using a TVZ basis set and experimental IR and Raman data. Increasing the size of the basis set may improve accuracy, but the expected deviation between calculated and experimental frequencies can vary. The calculations are performed in gas phase, while experiments are conducted in water, which likely affects mode locations. Users should anticipate that calculated frequencies may be higher than experimental ones, a common issue in DFT calculations. Selecting appropriate functionals and basis set sizes is crucial for optimizing spectral calculations.
greisen
Messages
75
Reaction score
0
Hi,

I am calculating the spectra of a small molecule - benzen with nitrogen group attach. I have some experimental data of the molecule IR and raman.
I use DFT B3LYP with TVZ as basis set when I compare the modes and are a lot of differences between the two.

1. Would it help to increase the size of the basis sets?
2. How big a deviation should one expect?

The calculation is in gas whereas the experiment is in water - that should change the location of some of the modes.

Any comments appreciated thanks in advance
 
Physics news on Phys.org
I assume that you are comparing the calculated frequencies with the experimental ones? If so, it is very likely that the calculated frequencies are somewhat higher than the experimental ones. Is this the difference you are seeing?
 
yes it is this difference. Is there a way to determine if one is going to use DFT which functionals to use and the size of the basis set in order to optimise the calculation?
 

Thread 'Prove that evolution is constant (Provide at least two arguments to support your position)'

I don't get how to argue it. i can prove: evolution is the ability to adapt, whether it's progression or regression from some point of view, so if evolution is not constant then animal generations couldn`t stay alive for a big amount of time because when climate is changing this generations die. but they dont. so evolution is constant. but its not an argument, right? how to fing arguments when i only prove it.. analytically, i guess it called that (this is indirectly related to biology, im...
View full post »

Similar threads

Finding Help with Computational Chemistry on PF
Replies
1
Views
1K
Molecular Modeling: Geometry Optimization, Vibration Analyses & More
Replies
1
Views
2K
I Effective Hamiltonian to Rotational Term Values
Replies
0
Views
3K
Frequencies of atoms/molecules
Replies
1
Views
2K
Chemistry Calculate persistence length of a single dsDNA molecule
Replies
3
Views
3K
Chemistry How do we know ##BF_3## has Lewis structure but ##Al_2S_3## does not?
Replies
1
Views
2K
Why Can a Sound Wave Not Travel Faster than the Average Molecule Speed?
Replies
23
Views
4K
Implementing “Ab initio” approach in molecular mechanics method
Replies
4
Views
2K
Chemistry How Fast Would a Nitrogen Molecule Travel with Photon Energy?
Replies
1
Views
2K
Chemistry Name the given Phenol organic molecule
Replies
5
Views
3K

Hot Threads

Recent Insights

Back
Top