Talk:Quantum chemistry

Wiki Education assignment: Physical Chemistry I Quantum Chemistry and Spectroscopy

This article was the subject of a Wiki Education Foundation-supported course assignment, between 26 August 2025 and 17 December 2025. Further details are available on the course page. Student editor(s): Ruaugustine, Lyonly4 (article contribs).

— Assignment last updated by Lyonly4 (talk) 14:02, 9 December 2025 (UTC)

Not correct edits

Sorry @Lyonly4, but there were too many problems in your edits so I reverted them. While those on MO were perhaps OK, you bundled them in with too many others:

1. MOS is no caps in section titles
2. Your statement "exchange principle being considered" is not right. E_xc is calculated using the spin-resolved densities in various approximations. Very common is exact exchange, Hubbard U etc
3. DFT calculates the energy as a sum of density terms and orbitals, not just the density. Please recheck KS theory.
4. Wave Functional Theory does not exist, plus as above you have misunderstood modern DFT.

Ldm1954 (talk) 16:18, 9 December 2025 (UTC)

Addendum, make smaller edits and suggest here for concensus first. Ldm1954 (talk) 16:19, 9 December 2025 (UTC)

Lead Image Idea: C₆H₆ delocalisation

I have heard that this article used to have a photograph of quantum chemist Linus Pauling as a lead image, but it was removed.

I’d like to propose an alternative that I think would suit the article well. The image I have in mind is a diagrammatic representation of electron delocalisation across the overlapping π orbitals of a benzene molecule, where the superposition of electron wavefunctions gives rise to the delocalised π‑electron cloud.

I originally came up with this idea for the collage on the physics article, but later decided not to use it because it was too chemistry-oriented. It only occurred to me today that it might be a much better fit here — not a bad way to start the new year.

Screenshot of article (in edit mode) with my lead image idea implemented.

When testing it in edit mode, the image integrates quite well into the lead (see screenshot above, along with the source code). The published version would look slightly different, but I expect it would render just as cleanly.

[[File:Electron delocalisation in a benzene molecule.png|thumb|right|[[Delocalized electron|Electron delocalisation]] across the overlapping [[Pi bond|π orbitals]] of a [[benzene]] [[molecule]], a quantum-chemical effect arising from the [[Superposition principle|superposition]] of electron [[Wave function|wavefunctions]].]]

Any thoughts?

Kind regards, Xyqorophibian (talk) 12:47, 1 January 2026 (UTC)

It seems good to me, but I wonder if it accurately reflects electron distribution. Jo-Jo Eumerus (talk) 11:00, 2 January 2026 (UTC)

Hi @Jo-Jo Eumerus.

To answer your question: not really.

The diagram isn’t meant to illustrate the spatial electron density — that’s usually done with 3D isosurface renders (such as the one below, though its quality isn’t ideal).

Its purpose is simply to indicate delocalisation schematically, which is why the skeletal structure is shown between the two discs. That combination makes it clear that the discs represent delocalised regions rather than density.

Given that it conveys the concept clearly and fits the article’s needs, I think it’s a suitable addition. If anyone has concerns or prefers an alternative, I’m happy to discuss.

Glad to hear the idea has been received positively.

Kind regards, Xyqorophibian (talk) 12:51, 2 January 2026 (UTC)

@Xyqorophibian: Well, one cannot know if an idea is received favorably based on one response. This aspect is one of the main challenges here in Wikipedia. Few editors (1), fewer who are confident of quantum concepts (2), fewer still who respond to queries (3). In contrast, there are probably many readers of this article. In any case, someone desperately needs to address the second figure, which is uselessly cryptic: "An anti-bonding molecular orbital of Butadiene". Maybe an energy diagram even for H₂ or H₃⁺.--Smokefoot (talk) 13:19, 5 January 2026 (UTC)

@Smokefoot: Hi, I'm aware that one person's acceptance doesn't equate an entire community's acceptance. And I'm glad more people are joining the discussion to work on this.

About the second image, are you referring to Trihydrogen-cation-MO-diagram.svg? I'm a bit confused because that image (the article's second image) is not an anti-bonding molecular orbital of Butadiene.

Kind regards, Xyqorophibian (talk) 00:20, 6 January 2026 (UTC)

The proposed image does not look factually correct due to different apparent vertical distance of "upper" pi to sigma vs "lower" pi to sigma. The chosen perspective also could be misinterpretted as a slip/skew of the upper pi to be off-center compared to the ring. DMacks (talk) 15:30, 5 January 2026 (UTC)

@DMacks: The intention here is to use a schematic illustration to accessibly introduce the idea of π‑electron delocalisation, rather than a geometrically precise depiction (e.g. an isosurface render) catered to readers already familiar with the topic.

I understand the concerns about the perspective suggesting slight asymmetry, but misinterpretations can be simply prevented by adding a note for clarity.

Kind regards, Xyqorophibian (talk) 00:48, 6 January 2026 (UTC)

I strongly object to using something that is known to be and visually obviously incorrect as an illustration of the very topic it's meant to illustrate. And it's even more factually incorrect than I first noted: even apart from the vertical positioning, the π clouds themselves do not have a correct (in the quantum chemical sense) geometry. The π₁ molecular orbital has a bulge in the vicinity of each atom's p (rather than the simple art of "delocalization"). DMacks (talk) 07:06, 8 January 2026 (UTC)

I should have noted that! It has no particular relevance to quantum chemistry. What about this one from Commons?

--Smokefoot (talk) 18:56, 5 January 2026 (UTC)

@Smokefoot: I'm afraid that image is actually less relevant to QC than the current one.

The current one is a direct example of quantum chemistry, merging ring structures (arising from pi bonds) in molecules to the superposition of wavefunctions (i.e. linearity of the Schrödinger equation). So, it incorporates both chemistry and quantum mechanics, making it a conceptually appropriate lead image.

This image is that of the electric potential field throughout a benzene molecule, making it an intersection of chemistry and electromagnetism rather than chemistry and quantum mechanics.

Kind regards, Xyqorophibian (talk) 01:02, 6 January 2026 (UTC)

How about File:HOMO-4 Benzol.jpg? DMacks (talk) 07:17, 8 January 2026 (UTC)

That’s a solid candidate. I’ve also come across an alternative that I think may serve the article even better, so I’ve uploaded and added it for consideration. Xyqorophibian (talk) 10:06, 8 January 2026 (UTC)

In terms of an image, I think a pseudocolor map of some type is better that the initial delocalisation image. That strikes me as a bit too schematic. However, I don't think either of the density maps above are good because they don't hit the sweet spot of being immediately understandable (KISS). I think an electron density difference plot would be better, perhaps even for something as simple as a single HF or water molecule. I could not find anything on the commons or elsewhere that is simple enough, it may need to be calculated which is not hard. (I sm no volunteering, I am furiously killing innocent electrons on my cluster to get results for a talk in two weeks.) A not great example is Fig 3 in http://dx.doi.org/10.1103/PhysRevB.74.085401. An ELFmap might be an alternative, they look pretty although I have never used one them myself. Ldm1954 (talk) 09:18, 8 January 2026 (UTC)

Yes.

Had the same idea and found a good image on conmmons, cropped it, reuploaded and was about to implement but had to pause and deal with something else. After returning, I've implemented it in.

Gonna make a full announcement about it as a separate talk page topic.

Kind regards, Xyqorophibian (talk) 10:19, 8 January 2026 (UTC)

New Lead Image!

Simulated electron localization function (ELF) map of a furan (C₄H₄O) molecule. Colour indicates the magnitude of the ELF field, which reflects the degree of electron localisation at each point in the molecular plane.

Hi all.

I previously suggested using a schematic of benzene with a delocalised π‑cloud as the lead image.

Following concerns raised by @DMacks about its visual clarity, I looked for alternative candidates, namely a simple pseudocolor map of a molecule. I found File:Furan ELF.svg, cropped it, and reuploaded it to Commons.

The image is a simulated electron localisation function pseudocolor map of a furan molecule. It provides a simple, intuitive representation of electron localisation based on real quantum‑chemical calculations, and seems to offer a clearer and more accurate lead image than a schematic delocalisation diagram. I have now implemented it into the article.

Kudos to @Ldm1954 for independently suggesting the same general approach.

If anyone has comments, objections, or suggestions, please feel free to discuss them here.

Kind regards, Xyqorophibian (talk) 10:39, 8 January 2026 (UTC)