Sir Cramer, I haven't any prior knowledge of computational chemistry. But I find Chemistry with computer science quite fascinating field. So I wanna begin learning this. So for the basics what should I follow?
Well, you need a good founding in general chemistry. You need some physics. You need some maths (calculus and linear algebra will be most what you need), and you need to research some software used in computational chemistry that you can download and apply your learning.
Hello Chris, I am hoping you (or anyone else more knowledgeable in the field than I) will see this comment and will be able to answer the following question: In the end of this video you describe how an experimentalist would use results from vibrational/rotational spectroscopy to empirically construct a potential energy surface. This process confuses me slightly; I understand that through experiment we can determine the relative energies of the physical states (corresponding to the y axis) but I do not see how information about the 'width' of the energy level is ascertained. I suppose that corresponds to the allowed bond-lengths for a certain energy state. Thus, I wonder how is the curvature of the function to be fit to experimental data determined? Or in other words, how do we determine what two x coordinates (critical bond lengths?) correspond with the measured y coordinate (energy)?
Happy to help. It still takes quantum chemistry, but now it is quantum chemistry subject to constraints. In particular, while the Schrödinger equation for a harmonic oscillator is exactly solvable, that is only a modest approximation for the true vibrational potential. A BETTER potential would be a polynomial of arbitrary degree, and that Schrödinger equation CAN be solved, albeit with numerical methods, in order to obtain all the (lower) energy levels. So, if you have a lot of spectroscopic data about the energy level separations, ideally including different isotopes (so different reduced masses in the Schrödinger equation), you then optimize the coefficients of a polynomial potential energy function for the bond stretch in order to minimize any error between predicted energy separations and observed ones. Of course, once you have the potential energy function that agrees with the observed energy separations, you also have the associated wave functions, so you can assess things like equilibrium bond lengths, average bond lengths, etc. That's the approach to which I was referring. (Note that you could also optimize coefficients for a Morse potential, for example -- the more constraints you have from spectroscopic measurements, the more accurately you can fit the potential energy curve.)
Great lectures! very clear and very helpful. Thank you!
Thanks!
Thank you.
Sir Cramer,
I haven't any prior knowledge of computational chemistry.
But I find Chemistry with computer science quite fascinating field.
So I wanna begin learning this. So for the basics what should I follow?
Well, you need a good founding in general chemistry. You need some physics. You need some maths (calculus and linear algebra will be most what you need), and you need to research some software used in computational chemistry that you can download and apply your learning.
Are these videos on a website? I find them really helpful but they are hard to navigate in your account. Thanks in advance!
pollux.chem.umn.edu/8021/Lectures/
Enjoy!
Hello Chris, I am hoping you (or anyone else more knowledgeable in the field than I) will see this comment and will be able to answer the following question:
In the end of this video you describe how an experimentalist would use results from vibrational/rotational spectroscopy to empirically construct a potential energy surface. This process confuses me slightly; I understand that through experiment we can determine the relative energies of the physical states (corresponding to the y axis) but I do not see how information about the 'width' of the energy level is ascertained. I suppose that corresponds to the allowed bond-lengths for a certain energy state. Thus, I wonder how is the curvature of the function to be fit to experimental data determined? Or in other words, how do we determine what two x coordinates (critical bond lengths?) correspond with the measured y coordinate (energy)?
Happy to help. It still takes quantum chemistry, but now it is quantum chemistry subject to constraints. In particular, while the Schrödinger equation for a harmonic oscillator is exactly solvable, that is only a modest approximation for the true vibrational potential. A BETTER potential would be a polynomial of arbitrary degree, and that Schrödinger equation CAN be solved, albeit with numerical methods, in order to obtain all the (lower) energy levels. So, if you have a lot of spectroscopic data about the energy level separations, ideally including different isotopes (so different reduced masses in the Schrödinger equation), you then optimize the coefficients of a polynomial potential energy function for the bond stretch in order to minimize any error between predicted energy separations and observed ones. Of course, once you have the potential energy function that agrees with the observed energy separations, you also have the associated wave functions, so you can assess things like equilibrium bond lengths, average bond lengths, etc. That's the approach to which I was referring. (Note that you could also optimize coefficients for a Morse potential, for example -- the more constraints you have from spectroscopic measurements, the more accurately you can fit the potential energy curve.)
Sir, You never mentioned about the higher order saddle points,. Isn't it more exact that the First order saddle point is the transition state?
Voice reminds me of Brian Greene. Same voice inflections