Schrodinger equation molecules

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Discussion Overview

The discussion focuses on the formulation of the Schrödinger equation for a mixture of hydrogen (H2) and helium (He) molecules, specifically addressing how to write the full equation pre-approximation, including the specification of potentials and the Hamiltonian. The scope includes theoretical aspects of quantum mechanics and the challenges of solving the equation for multi-particle systems.

Discussion Character

  • Exploratory, Technical explanation, Debate/contested

Main Points Raised

  • One participant seeks to write the full Schrödinger equation for a mixture of 75% H2 and 25% He, asking about the specifics of specifying potentials and the Hamiltonian.
  • Another participant suggests that the general approach involves each particle moving in the potential of all other particles, noting the need for multiple position vectors corresponding to nuclei and electrons.
  • A different viewpoint argues against writing the Schrödinger equation for a mixture, proposing that one should sum the electrons and nuclei to write a Hamiltonian with Coulomb potentials between pairs.
  • There is a question about the number of position vectors needed, with one participant suggesting a discrepancy in counting nuclei and electrons.
  • Concerns are raised about the implications of having discrete mixtures and whether different mixtures would yield identical properties.
  • Participants discuss the challenges of solving the Schrödinger equation for multi-particle systems, emphasizing the use of perturbation theory and the intractability of finding solutions for more than one particle without approximations.
  • One participant expresses a desire to see the full form of the equation to understand the approximations that follow, despite recognizing the complexity involved.
  • Another participant compares the situation to the three-body problem in classical mechanics, noting that while solutions exist, they cannot be derived from the full equations.
  • There is a discussion about the role of the Hamiltonian in the Schrödinger equation and the absence of wave-functions in the provided document, leading to confusion about transitioning from the Hamiltonian to the equation form.

Areas of Agreement / Disagreement

Participants express differing views on how to approach the formulation of the Schrödinger equation for mixtures, with no consensus on whether a discrete number of mixtures leads to identical properties. The discussion remains unresolved regarding the specifics of writing the equation and the implications of the Hamiltonian's form.

Contextual Notes

Participants acknowledge the limitations of directly solving the Schrödinger equation for complex systems and the necessity of approximations, but they do not reach a consensus on the best approach to formulate the equation or the implications of the Hamiltonian.

  • #31
So in SI units all I have to do with the kinetic energy term, bracketed T_n, is replace it with this:

- \sum^M_{A=1} ({\frac{h^2 \cdot m_e}{2 \cdot m_A} \cdot \nabla_A^2})

Where m_e is the mass of an electron, m_A is the mass of nucleus A and h (sorry I couldn't find h bar but that's what I meant) is the reduced Planck constant.

And put that into the second Hamiltonian and I would have created a complete SI unit version of the first?
 
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  • #32
Big-Daddy you seem to have some very big misunderstandings. What book have you been studying quantum from?
 
  • #33
I don't study quantum mechanics on its own yet. I have just read the chapters in Atkins' Physical Chemistry.

Is my above expression correct?
 
  • #34
Big-Daddy said:
I don't study quantum mechanics on its own yet. I have just read the chapters in Atkins' Physical Chemistry.

Is my above expression correct?
If it is supposed to be kinetic energy, what are the units on the expression you put forth?

In any event, physical chemistry texts are really horrid on the whole at introducing quantum mechanics. If you want a book that is better, but still chemistry oriented, I'd recommend getting McQuarrie's Quantum Chemistry.
 
  • #35
Sorry, I noticed my answer isn't dimensionally sound. How about this one:

- \sum^M_{A=1} ({\frac{h^2}{2 \cdot m_A} \cdot \nabla_A^2})

I will look into certain books which show some development of more quantum ideas.
 
  • #36
Big-Daddy said:
Sorry, I noticed my answer isn't dimensionally sound. How about this one:

- \sum^M_{A=1} ({\frac{h^2}{2 \cdot m_A} \cdot \nabla_A^2})

I will look into certain books which show some development of more quantum ideas.
Close, it should be hbar but otherwise, so long as M is the number of particles in the system, that is fine.
 
  • #37
Thanks. And is energy (when we solve for it) a function of the position, or a numerical value for the system as a whole?
 
  • #38
Big-Daddy said:
Thanks. And is energy (when we solve for it) a function of the position, or a numerical value for the system as a whole?
It's the latter.
 

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