Predicting Vibrational Shifts

  • Thread starter knghrts17
  • Start date
In summary, the conversation discusses the possibility of using first-principles calculations to predict the peaks in vibrational spectroscopy studies involving adsorbates on the surface of CNT. There is some disagreement on the accuracy of these predictions, as quantum-chemical software may not accurately reproduce certain forces. However, there is ongoing research and development in this area. It is suggested that a collaboration with experts in theoretical chemistry may be beneficial for those interested in using first-principles calculations for this purpose.
  • #1
knghrts17
11
0
Hello all,


We are currently in the middle of a study involving adsorbates on the surface of CNT using vibrational spectroscopy. I don't have much experience with this, but I was wondering if it is possible to predict the peaks using first-principles calculations? If so would anyone be willing to share this information (i.e a source)?

Thanks in advance
 
Physics news on Phys.org
  • #2
Well, you can calculate anything from first principles.. in principle! :)

But in general, QM calculations don't do a terrific job of predicting shifts. Which isn't to say they can't be useful though. Depends also entirely on how you do it. Most quantum-chemical software can calculate vibrational spectra through a variety of methods, the simplest being a time-independent solution to the equilibrium position, and then calculate the second-order derivatives of the energy w.r.t. atomic coordinates (a harmonic oscillator approximation). I think there are also various approximate methods for getting anharmonic corrections. The best way is of course to work with the time-dependent equation. It also depends on the nature of the vibrational bonds in question. I.e. DFT methods tend not to reproduce van der Waals forces correctly - which may be a big issue if you're talking about nanotubes.

There's a lot of development in this within theoretical chemistry. In short, it's still pretty far from being a 'black box' method where you can just insert a model and get good values. If you're serious about doing it though, I'd suggest considering a collaboration with one of the many who study this stuff full-time.
 
  • #3
alxm,

One does not need to work with the time-dependent S.E to solve for the natural vibration frequencies of the absorbate. Using the harmonic approximation, one can predict the natural vibration frequency shift of the absorbate on the CNT surface. The simplest assumption is to assume that the absorbate vibrates independently of the CNT.

modey3
 

1. What is the purpose of predicting vibrational shifts?

The purpose of predicting vibrational shifts is to understand the changes in the vibrational frequencies of molecules due to external factors such as temperature, pressure, and chemical environment. This can provide valuable insights into the behavior and properties of molecules, as well as aid in the design of new materials with desired properties.

2. How do scientists predict vibrational shifts?

Scientists use various computational methods, such as density functional theory (DFT) and coupled cluster theory, to calculate the vibrational frequencies of molecules and predict how they will change under different conditions. These methods involve solving the Schrödinger equation to determine the energy levels and frequencies of the vibrational modes of the molecule.

3. What factors can affect vibrational shifts?

Vibrational shifts can be affected by several factors, including temperature, pressure, and chemical environment. Changes in these conditions can alter the potential energy surface of the molecule, leading to changes in the vibrational frequencies. Other factors such as molecular geometry, bond strength, and electronic structure can also have an impact on vibrational shifts.

4. How accurate are predictions of vibrational shifts?

The accuracy of predicting vibrational shifts depends on the computational methods used and the complexity of the molecule. Generally, DFT calculations can provide accurate predictions for simple molecules, whereas more advanced methods may be needed for larger or more complex molecules. However, experimental validation is always necessary to confirm the accuracy of the predictions.

5. What are the applications of predicting vibrational shifts?

Predicting vibrational shifts has many applications in fields such as chemistry, materials science, and pharmaceuticals. It can help researchers understand the behavior and properties of molecules, design new materials with specific properties, and optimize chemical reactions. In pharmaceuticals, it can aid in drug development and predicting the stability and reactivity of drug molecules under different conditions.

Similar threads

  • Atomic and Condensed Matter
Replies
9
Views
4K
  • Atomic and Condensed Matter
Replies
7
Views
1K
  • Atomic and Condensed Matter
Replies
12
Views
2K
  • Atomic and Condensed Matter
Replies
0
Views
366
  • Atomic and Condensed Matter
Replies
1
Views
1K
  • Atomic and Condensed Matter
Replies
1
Views
1K
  • MATLAB, Maple, Mathematica, LaTeX
Replies
1
Views
1K
Replies
1
Views
643
  • Atomic and Condensed Matter
Replies
1
Views
1K
  • Biology and Medical
Replies
5
Views
841
Back
Top