Ken G said:
Clearly quantum chemistry is a whole lot like quantum physics, which is what you seem to be stressing. I think the questioner wants distinctions.
No, you seem to miss the point entirely. Quantum chemistry is
not 'like' quantum physics. It's an
application of quantum physics to molecules, just as solid-state physics modelling is to crystals, and nuclear physics is to nucleons, and so forth.
You have to study quantum physics
before you can learn quantum chemistry. I'm not sure why this would be so hard to grasp. You have to study QM before you can learn the methods and math to calculate band gaps in solid-state (and that too, is a specialized application), and so for HOMO/LUMO energies in quantum chemistry. (Those two concepts are in fact
the same thing, and calculated using essentially the
same methods)
If someone's got a textbook on quantum chemistry without having studied QM before (Is it Levine's book?), then it's almost certainly an introductory textbook that first contains a run-through of basic of QM before going into basic QC. But anyone wanting to specialize in QC will need to know grad-level quantum mechanics.
That's not a very realistic position. You might as well state that all of physics requires quantum mechanics to understand, for exactly the same reasons.
No, because there's a classical theory of physics, which is applicable in some situations. There
is no 'classical' theory of chemistry whatsoever. That does not mean (non-quantum) chemists know or use the formalism and math of quantum mechanics, though.
I'm sure the same is true for chemists, most of whom recall quantum mechanics from the last time they taught quantum chemistry and little else-- just like most physicists.
Most chemists
don't know any quantum chemistry! It's a sub-field. And most quantum chemists are actually
physicists. My PhD is in physics ("chemical physics"). My old supervisor's doctorate (and his old supervisor's doctorate, in turn) was in "theoretical physics". I currently work on a physics faculty. The field is an offshoot of theoretical physics,
not of chemistry, because again: There
was no real theory of chemistry prior to QM. The pioneers of QC were Heitler, London, Slater, Mulliken, Pauling, Hund, Born, etc.. All physicists, mainly theoretical physicists.
The reason why it's long been mostly physicists, is precisely because most chemistry students are a bit loath to study up on the prerequisite level of math and QM.
I didn't mean to suggest chemists were less intelligent or less rigorous in what they do.
I didn't think you did. But the difference here is that ordinary chemists learn conceptual, approximate models (VB/MO theory). Those are rigorously based on QM, but they don't learn the derivations or math behind it (unless they actually go into QC, which as I said, requires that you learn QM first). There's no real math with those models, because they're not quantitative. That's not considered quantum chemistry as much as standard
chemical theory. It's known by every chemist, and used by most of them, with the only exception perhaps being some biochemists who are studying things that don't have to do so much with chemical bonding and reactivity.
But quantum chemistry is
not taught like chemistry. It's taught like physics. It most certainly does involve the fundamentals. In a QC textbook, everything is derived mathematically from first principles, in the same manner it is in any physics textbook where quantum theory is applied to more in-depth modelling applications. Is http://arxiv.org/abs/1108.1104" quantum chemistry or solid-state physics? It's
both, in fact. But it's not actual chemistry.