What Are the Applications of Quantum Mechanics in Chemistry?

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Discussion Overview

The discussion centers on the applications of quantum mechanics in chemistry, particularly regarding the calculation of molecular orbitals, isomers, and reaction predictions. Participants explore theoretical frameworks and computational methods used in quantum chemistry, touching on both foundational principles and current practices.

Discussion Character

  • Exploratory
  • Technical explanation
  • Conceptual clarification
  • Debate/contested
  • Mathematical reasoning

Main Points Raised

  • Some participants propose that quantum mechanics underpins all of chemistry, suggesting that chemistry can be viewed as applied quantum mechanics.
  • There is a discussion about the feasibility of calculating molecular orbital diagrams for all energetically likely isomers based on atomic and electronic configurations.
  • Participants mention the importance of the Schrödinger equation in determining molecular structures and the need for approximations in practical calculations.
  • Some contributions highlight the current state of quantum chemistry, noting that while foundational examples like the hydrogen atom are well understood, more complex systems are less frequently addressed in educational materials.
  • There is mention of computational methods such as path integral quantum mechanics and density functional theory (DFT) as tools for addressing complex chemical problems.
  • Questions arise about how to specify the necessary information for the Schrödinger equation to derive molecular structures and their energetic properties.
  • Participants express interest in resources or fields of study that focus on the development of methods for calculating molecular properties at a quantum mechanical level.

Areas of Agreement / Disagreement

Participants generally agree on the foundational role of quantum mechanics in chemistry, but there is no consensus on the specific methodologies or the current state of computational practices in the field. Multiple competing views on the best approaches and resources remain evident.

Contextual Notes

Limitations include the reliance on approximations in quantum chemistry calculations, the challenge of addressing many-body interactions, and the varying levels of complexity in educational resources available to students.

Who May Find This Useful

This discussion may be useful for students and researchers interested in the intersection of quantum mechanics and chemistry, particularly those seeking to understand molecular structure calculations and the theoretical underpinnings of quantum chemistry.

  • #31
Big-Daddy said:
I've read the page you linked on the Born-Oppenheimer approximation. However, I'm still confused as to what you mean by "molecular structure and isomers have no meaning at a fully quantum mechanical level" - surely there must be something to distinguish isomers from each other at the most fundamental level, since they are indeed different species and we can isolate them separately from one another in the lab?

Isomers can isomerize. On a most fundamental level, the eigenstates of the full hamiltonian are superpositions of different isomers.
The question why we really observe isomers is far from trivial. Probably it is due to interactions with neighbouring molecules, so it is a colligative effect. You may want to google for Hund's paradox.
 
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  • #32
DrDu said:
Isomers can isomerize. On a most fundamental level, the eigenstates of the full hamiltonian are superpositions of different isomers.
The question why we really observe isomers is far from trivial. Probably it is due to interactions with neighbouring molecules, so it is a colligative effect. You may want to google for Hund's paradox.

Doesn't Hund's paradox just apply to chiral systems? I thought his question was more about non-degenerate isomers (boat versus chair and all that).
 
  • #33
Einstein Mcfly said:
Doesn't Hund's paradox just apply to chiral systems? I thought his question was more about non-degenerate isomers (boat versus chair and all that).

Yes, but as always, for degenerate states the consideration of superpositions is most relevant.
 

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