How to find vibrational frequency for specific bond? (DFT)

In summary, the conversation discusses the difficulties in identifying the frequency corresponding to the stretching of a phosphorus carbon double bond in a compound with the formula C39H41PS2. The speaker mentions performing an optimization and frequency calculation at the ub3lyp 6-311g level of theory and using Molden to analyze the results. They express difficulty in finding the desired frequency and inquire about obtaining this information directly from the output file. The response suggests looking at the list of normal vibrations and the contribution of individual atoms in the output to identify the relevant normal modes.
  • #1
Dan Zar
9
0
Hello,
I performed an optimization and frequency calculation at the ub3lyp 6-311g level of theory. The compound has the formula C39H41PS2. Using Molden, I am having a hard time identifying the frequency corresponding to the stretching of a phosphorus carbon double bond present in the molecule. I expect the frequency to be very low in intensity which makes my task harder. I am wondering if there is any way to obtain this information directly from the output file without having to click every frequency on Molden. Thank you very much.
upload_2016-5-5_18-56-52.png
 
Physics news on Phys.org
  • #2
The calculation does not give you a value for the stretching of only this bond. Rather this stretching will contribute to several normal modes. Looking at the output of your calculation, you should see a list of the normal vibrations and the contribution of the individual atoms. Identify those normal modes where the C and P atom in question make a large contribution.
 

1. How does DFT calculate the vibrational frequency for a specific bond?

DFT (Density Functional Theory) calculates the vibrational frequency for a specific bond by solving the Schrödinger equation and using the Hessian matrix, which contains information about the potential energy surface of the molecule.

2. What is the role of the Hessian matrix in calculating vibrational frequency using DFT?

The Hessian matrix, also known as the force constant matrix, contains information about the second derivatives of the molecule's potential energy with respect to the atomic coordinates. This information is used to calculate the vibrational frequencies of the molecule.

3. How accurate is DFT in predicting vibrational frequencies for specific bonds?

DFT has been shown to be accurate in predicting vibrational frequencies for specific bonds, with an average error of less than 5%. However, the accuracy can vary depending on the specific functional and basis set used.

4. Can DFT be used for all types of bonds?

Yes, DFT can be used for all types of bonds, including single, double, and triple bonds. It can also be used for non-bonded interactions such as hydrogen bonding.

5. Are there any limitations to using DFT for calculating vibrational frequencies?

While DFT is a powerful tool for predicting vibrational frequencies, it does have some limitations. One limitation is that it assumes the molecules are in their ground state, so it may not accurately predict frequencies for excited states. Additionally, the accuracy of DFT can be affected by the choice of functional and basis set, as well as the size of the molecule being studied.

Similar threads

Implementing “Ab initio” approach in molecular mechanics method
    • Chemistry
Replies
4
Views
1K
A Why does my chosen basis set for W crash (DFT)?
    • Atomic and Condensed Matter
Replies
1
Views
2K
Finding Help with Computational Chemistry on PF
    • Chemistry
Replies
1
Views
886
A How can I tell Gaussian to read coordinates as Cartesian?
    • Atomic and Condensed Matter
Replies
1
Views
2K
How to get specific frequency and time values for .wav file
    • MATLAB, Maple, Mathematica, LaTeX
Replies
2
Views
2K
Frequencies of atoms/molecules
    • Chemistry
Replies
1
Views
2K
How Raman Spectroscopy works?
    • Atomic and Condensed Matter
Replies
5
Views
5K
On carbon, methane and electromagnetic radiation
    • Electromagnetism
Replies
2
Views
2K
Chemistry Chemistry: Elements, Molecules and Bonds
    • Biology and Chemistry Homework Help
Replies
1
Views
6K
Why are specific heat high in water but low in ethylene glycol?
    • Thermodynamics
Replies
5
Views
8K

Hot Threads

Recent Insights

Back
Top