Quantum Chemistry or Quantum Physics?

[BioCore]

I was wondering if someone could tell me what exactly is the difference between Quantum Chemistry and Quantum Physics? Whenever I look in a Chemistry textbook, I see Quantum Chemistry and the latter is true for Physics - yet strangely enough I see most of the information is quite similar. Although maybe I have never delved deeply enough into the texts to be able to see the difference.

So is there any big difference or do the two fields just approach the topic of Quantum theory differently?

 

[maverick_starstrider]

Well quantum chemistry and quantum physics definately overlap but a quantum chemistry book will most likely be less theoretical and less concerned with mathematical rigour and more concerned with 'real world' applications and such. And might for example spend a lot more time talking about the zeeman effect and NMR where a quantum physics book might spend more time talking about rigged hilbert space and operator theory

 

[BioCore]

Oh I see, that makes sense. Would you say that someone studying chemistry (specifically Biotechnology/Biochemistry) could benefit with some study of the Physics of such topics, or is this more of a waste of time?

 

[maverick_starstrider]

I'd say it's a waste of time. Physicists always complain about the lack of rigour (and the lack of a strong theoretical framework) in things like bio (and mathematicians complain about lack or rigour in physics) but the truth is bio students don't learn physical theory (and instead are often taught incorrect but ultimately 'good enough' rules of thumb and such) because it takes a long time to teach it and there are few fields of bio where it will ever come up.

 

[maverick_starstrider]

That being said, I still reserve the right to scoff at things like drawing a lipid bilayer as a bunch of balls with squigly tails and saying 'like the squigly line hates water and like the ball likes it'. :)

Cheers

 

[quantumdude]

I've taken both quantum chemistry and quantum physics. Both started out with basic wave mechanics, but then the chem course focused on atoms and molecules while the physics course went into the dirac formalism, time evolution, angular momentum, symmetry, and scattering. Both courses contained perturbation theory and the variational method.

 

[BioCore]

Tom thanks for the input, now I can generally see that Quantum Physics is something more of what I would like to study.

 

[maverick_starstrider]

I've taken both quantum chemistry and quantum physics. Both started out with basic wave mechanics, but then the chem course focused on atoms and molecules while the physics course went into the dirac formalism, time evolution, angular momentum, symmetry, and scattering. Both courses contained perturbation theory and the variational method.

Really? The quantum chem course didn't teach Bra-Ket notation?

 

[Fearless]

maverick_starstrider: Dear Sir, I must object to the notion that biochemists doesn't need QC or QM.

It is actually very useful and explains such random things like why lykopene is red/orange and stuff like that.

For the more hardcore stuff, it's very useful for the pharmaceutical industry and calculations on bio-molecules that tend to be very big.

Biocore: I think you should take a QC course. You will find it useful.

 

[Asphodel]

Really? The quantum chem course didn't teach Bra-Ket notation?

...I had that stuff in my first year general physics course.

You may not need quantum physics, but quantum chemistry (or physical chemistry as it's sometimes labeled) should be a strong consideration for anyone in a chemical program if it's not already required. You can add the QM physics courses later (or earlier) if you have a strong interest.

 

[Howers]

Quantum chemistry is applying quantum mechanics to chemical problems. Quantum physics gives you the whole story in a more mathematical form. I'd say study some quantum chemistry if you're in bio, and even that is over kill. Doing quantum physics is over over kill, and most of it you won't find very useful because it is highly abstract and not very practical. So chemists devised their own spin where you study only the stuff needed for chemistry.

As an analogy, do you need the foundations of language and linguistics to read and write english? Certainly not. Neither do you need quantum mechanics to be working with atoms. Ofcourse, every bit helps if you really want to change the world. But that should be studied independently, and not as something to deter you from your main goal - biology.

 

[Asphodel]

As an analogy, do you need the foundations of language and linguistics to read and write english?

Some of it, which is why they traditionally bother with things like Greek and Latin roots.

 

[malawi_glenn]

chemistry is just a big sub-branch of physics.. atoms and molecules etc.

 

[Kurdt]

Some of it, which is why they traditionally bother with things like Greek and Latin roots.

Thats strange because English is a Germanic language.

To the OP. Both courses will be similar. You obviously need a foundation in quantum mechanics before you can apply it to anything so that will most likely be exactly the same as a lower undergrad physics course. Where things will chage however is that quantum chemistry will remain focused on applications (i.e. molecular quantum mechanics) physics classes will move on to QCD and QFT and perhaps re-introduce the subject in terms of a more modern derivation along the lines of Sakurai's book rather than the historical approach.

 

[sam432]

have you considered Quantum Quantum?

 

[Howers]

chemistry is just a big sub-branch of physics.. atoms and molecules etc.

Wrong. Most of chemistry makes no refrence to physics. Atoms were known to exist before any quantum mechanics were used to describe them. Reactions were studied by measuring relative masses of different compounds, and crystals were used to deduce structures. In fact, that is how most of chemistry is continued to be studied.

Physical chemistry is a sub-branch of physics. This is where we deal with physical notions of thermodynamics and electricity, and study the motion of molecules via quantum theory. Using your logic, biology is a sub-branch of chemistry (pfft, atoms and enzymes) and physics is a sub-branch of math(pfft equations and numbers). Physicists known squat about chemistry.

 

[Kurdt]

Still took a physicist to sort out the periodic table of elements for you.

 

[Howers]

Chemists need to leave trivial stuff to physicists to make them feel important.

 

[ekrim]

Using your logic, biology is a sub-branch of chemistry (pfft, atoms and enzymes) and physics is a sub-branch of math(pfft equations and numbers).

Dont forget that math is just a sub branch of philosophy (pfft just logic and crap)

 

[malawi_glenn]

i) Chemistry is a sub-branch of physics in that sense that chemistry deals with the electromagnetic force. All atoms and molecules etc. are interacting due to this force, and every reaction in chemistry can in principle be formulated as interactions on electrodynamical basis. Chemistry has, however, developed more efficient methods to deal with many of these reactions. A chemical reaction is just electrons chaning configuration in energy-space.

This is from wikipedia:
"Chemistry (from Egyptian kēme (chem), meaning "earth"[1]) is the science concerned with the composition, structure, and properties of matter, as well as the changes it undergoes during chemical reactions.[2] Historically, modern chemistry evolved out of alchemy following the chemical revolution (1773). Chemistry is a physical science related to studies of various atoms, molecules, crystals and other aggregates of matter whether in isolation or combination, which incorporates the concepts of energy and entropy in relation to the spontaneity of chemical processes.

Disciplines within chemistry are traditionally grouped by the type of matter being studied or the kind of study. These include inorganic chemistry, the study of inorganic matter; organic chemistry, the study of organic matter; biochemistry, the study of substances found in biological organisms; physical chemistry, the energy related studies of chemical systems at macro, molecular and submolecular scales; analytical chemistry, the analysis of material samples to gain an understanding of their chemical composition and structure. Many more specialized disciplines have emerged in recent years, e.g. neurochemistry the chemical study of the nervous system (see subdisciplines)."

Measuring the mass of something, isn't mass a physical quantity?... ;-)

ii) Physics is not a sub-branch of math, math is the language of physics. Physics deal with the real world, physics is also an experimental science. Math is just constructing a coherent logical 'language' to describe and relate quantities.

So saying physics is a subbranch of math, is like saying that politics is just a subbranch of English..

 

[will.c]

http://xkcd.com/435/

As a physicist, I agree that (theoretical) physics is a subfield of mathematics. There's plenty of non-empirical physics that goes on - look at string theory!

 

[maverick_starstrider]

Physicists know squat about chemistry.

This is true.

 

[Asphodel]

look at string theory!

People hold that up as an example very often when trying to make a categorical statement about physics. I don't think many of them have asked a physics professor about the current view of string theory among professional physicists (especially the philosophy prof I had that was trying to use it as a strawman and also going on about consciousness being necessary to collapse the wavefunction...interesting class there, since it was rather discussion oriented and I'd already studied a fair bit of QM). Anyway, the few I've talked to about it seemed to regard it as a more-or-less dead endeavor. I don't know how typical this is, but it was interesting.

 

[maverick_starstrider]

The whole thing is pretty much (hilariously) summed up here:

http://www.xkcd.com/435/

 

[Kurdt]

That link was posted three posts ago.

 

[will.c]

You must not have talked to the right professors. String theory is alive and well. It's gotten to the point where professional physicists who aren't working on it mostly don't care that much, but that doesn't make it a dead field.

Also, I wasn't trying to make a categorical statement about all of physics; I'm just saying there's a healthy subset of people in physics who are rationalists, enough so that you can't regard physics as a purely empirical endeavor since Newton. This means that the condescending "math is just the language of physics" attitude (as if we could make up our own, but chose reason for convenience!) is also an incorrect categorization of physics.

 

[Asphodel]

It's gotten to the point where professional physicists who aren't working on it mostly don't care that much

That would explain the effect I was seeing.

 

[Howers]

i) Chemistry is a sub-branch of physics in that sense that chemistry deals with the electromagnetic force. All atoms and molecules etc. are interacting due to this force, and every reaction in chemistry can in principle be formulated as interactions on electrodynamical basis. Chemistry has, however, developed more efficient methods to deal with many of these reactions. A chemical reaction is just electrons chaning configuration in energy-space.

This is from wikipedia:
"Chemistry (from Egyptian kēme (chem), meaning "earth"[1]) is the science concerned with the composition, structure, and properties of matter, as well as the changes it undergoes during chemical reactions.[2] Historically, modern chemistry evolved out of alchemy following the chemical revolution (1773). Chemistry is a physical science related to studies of various atoms, molecules, crystals and other aggregates of matter whether in isolation or combination, which incorporates the concepts of energy and entropy in relation to the spontaneity of chemical processes.

Disciplines within chemistry are traditionally grouped by the type of matter being studied or the kind of study. These include inorganic chemistry, the study of inorganic matter; organic chemistry, the study of organic matter; biochemistry, the study of substances found in biological organisms; physical chemistry, the energy related studies of chemical systems at macro, molecular and submolecular scales; analytical chemistry, the analysis of material samples to gain an understanding of their chemical composition and structure. Many more specialized disciplines have emerged in recent years, e.g. neurochemistry the chemical study of the nervous system (see subdisciplines)."

Measuring the mass of something, isn't mass a physical quantity?... ;-)

ii) Physics is not a sub-branch of math, math is the language of physics. Physics deal with the real world, physics is also an experimental science. Math is just constructing a coherent logical 'language' to describe and relate quantities.

So saying physics is a subbranch of math, is like saying that politics is just a subbranch of English..

Chemists do not derive their results from first principles of physics. The structure an atom and particles is the work of nuclear physicists and not chemists. A chemist uses this knowledge as a basis to study matter, between various substances.

Physical sciences doesn't mean physics, its a broad term grouping all the inorganic sciences together. Most of chemistry does not make refrence to electrostatics when dealing with reactions. They study a reaction and its products in the lab, and try to describe them. Physical chemistry has been included in the analysis to apply the laws of physics, so that's why we have all of our electron diagrams. But every science applies the laws of physics to give a more rigorous desription of their theories, but that does not mean said science is a branch of physics.

A chemist will study physical notions of matter such as mass, heat, or light. But they will not be concerned with their fundamental properties. Just like a biologist studying photosynthesis probably won't know the mathematical details of light. So a lot of scientists will apply physics, but won't be concered with where the physics came from. Physicists do the same thing with math.

That is why it is incorrect to call chemistry a sub-field of physics. An exception can be made with physical chemistry. These are chemists (or more appropriately physicists) that are very well versed with math and physics, and try to express the results of chemistry in terms of physics.

 

[maverick_starstrider]

There are also chemical physicists.

 

[Howers]

i) Chemistry is a sub-branch of physics in that sense that chemistry deals with the electromagnetic force. All atoms and molecules etc. are interacting due to this force, and every reaction in chemistry can in principle be formulated as interactions on electrodynamical basis. Chemistry has, however, developed more efficient methods to deal with many of these reactions. A chemical reaction is just electrons chaning configuration in energy-space.

This is from wikipedia:
"Chemistry (from Egyptian kēme (chem), meaning "earth"[1]) is the science concerned with the composition, structure, and properties of matter, as well as the changes it undergoes during chemical reactions.[2] Historically, modern chemistry evolved out of alchemy following the chemical revolution (1773). Chemistry is a physical science related to studies of various atoms, molecules, crystals and other aggregates of matter whether in isolation or combination, which incorporates the concepts of energy and entropy in relation to the spontaneity of chemical processes.

Disciplines within chemistry are traditionally grouped by the type of matter being studied or the kind of study. These include inorganic chemistry, the study of inorganic matter; organic chemistry, the study of organic matter; biochemistry, the study of substances found in biological organisms; physical chemistry, the energy related studies of chemical systems at macro, molecular and submolecular scales; analytical chemistry, the analysis of material samples to gain an understanding of their chemical composition and structure. Many more specialized disciplines have emerged in recent years, e.g. neurochemistry the chemical study of the nervous system (see subdisciplines)."

Measuring the mass of something, isn't mass a physical quantity?... ;-)

ii) Physics is not a sub-branch of math, math is the language of physics. Physics deal with the real world, physics is also an experimental science. Math is just constructing a coherent logical 'language' to describe and relate quantities.

So saying physics is a subbranch of math, is like saying that politics is just a subbranch of English..

Chemists do not derive their results from first principles of physics. The structure an atom and particles is the work of nuclear physicists and not chemists. A chemist uses this knowledge as a basis to study matter, between various substances.

Physical sciences doesn't mean physics, its a broad term grouping all the inorganic sciences together. Most of chemistry does not make refrence to electrostatics when dealing with reactions. They study a reaction and its products in the lab, and try to describe them. Physical chemistry has been included in the analysis to apply the laws of physics, so that's why we have all of our electron diagrams. But every science applies the laws of physics to give a more rigorous desription of their theories, but that does not mean said science is a branch of physics.

A chemist will study physical notions of matter such as mass, heat, or light. But they will not be concerned with their fundamental properties. Just like a biologist studying photosynthesis probably won't know the mathematical details of light. So a lot of scientists will apply physics, but won't be concered with where the physics came from. Physicists do the same thing with math.

That is why it is incorrect to call chemistry a sub-field of physics. An exception can be made with physical chemistry. These are chemists that are very well versed with math and physics, and try to express the results of chemistry in terms of physics.

 

[PipBoy]

chemistry is just a big sub-branch of physics.. atoms and molecules etc.

And Physics is just a large sub-branch of maths, which itself is just a sub-branch of philosophy...lets not get into patronising.

 

[jtbell]

Just out of curiosity, how did you find this thread which has been dormant for nearly two years?