Molecular Orbital Diagrams, learning how to draw?

[ApeXaviour]

Hi,
So I'm a phd student of physics, but my research overlaps a little with inorganic chemistry, specifically transition metal oxides and spectroscopies of them. I can glean some information MO diagrams and find them quite useful when writing about what I'm doing... however it's difficult to find ready made MO diagrams for all the compounds I'm studying, and if I do they're rather inconsistent in design thus making my papers/reports/thesis look messy.

I've been told however that they're relatively easy to draw by oneself, just a few rules to follow and a few properties to know.

Any chemistry books I've glanced at are either too basic and don't go into enough detail, or they're too complicated and assume you know how to make them already.

Any chance someone can recommend me a book that details the basic rules of drawing these? e.g. for IrO2?

Cheers :)

Declan

 

[SpectraCat]

Hi,
So I'm a phd student of physics, but my research overlaps a little with inorganic chemistry, specifically transition metal oxides and spectroscopies of them. I can glean some information MO diagrams and find them quite useful when writing about what I'm doing... however it's difficult to find ready made MO diagrams for all the compounds I'm studying, and if I do they're rather inconsistent in design thus making my papers/reports/thesis look messy.

I've been told however that they're relatively easy to draw by oneself, just a few rules to follow and a few properties to know.

Any chemistry books I've glanced at are either too basic and don't go into enough detail, or they're too complicated and assume you know how to make them already.

Any chance someone can recommend me a book that details the basic rules of drawing these? e.g. for IrO2?

Cheers :)

Declan

Why not just calculate them using an electronic structure package? Then you can use high-quality computer generated plots of the molecular orbitals. I would not really agree that it is "relatively easy" to generate accurate representations of MO's by hand. MO's basically represent how much the atomic orbitals on the component atoms are mixed in a given chemical compound ... you can use the symmetry of the molecule along with some rules of thumb to sketch rough representations of what the MO's might look like based on the phases of the different lobes of the component atomic orbitals and how they overlap, but they will only be approximately correct at best. One issue that is hard to deal with properly when sketching by hand is that the relative energies of the atomic orbitals affect the extent to which they will be able to mix when forming the MO's .. the closer the energies, the greater the extent of mixing. This can results in qualitative differences in the shapes of the MO's that you generate.

Anyway, that is why I suggested using a computational chemistry package (like Gaussian) to generate your MO images.

 

[ApeXaviour]

Why not just calculate them using an electronic structure package?

Thanks... initially that sounded great (get software to do it for me) so I took your advice. However, now it seems like it'd be quite a bit of overkill and a time-sink. I borrowed a copy of Spartan there and had a good play with it. It doesn't really appear designed for constructing bulk crystal structures, rather individual molecules (unlike for example VESTA). Nor could I find anything in the user guide that hinted at being able to create even a basic box and line MO energy-level diagram... it seems much more geared towards DFT and the like.

you can use the symmetry of the molecule along with some rules of thumb to sketch rough representations of what the MO's might look like based on the phases of the different lobes of the component atomic orbitals and how they overlap, but they will only be approximately correct at best.

I think that would do me... I really just need to be able to draw or produce simple diagrams like this for TiO2: http://imgur.com/CfTfg

I was just wondering if you knew of any literature that guided one through those rules of thumb to generate such diagrams? (or if you knew more basic software that did a rough job of it?).

 

[SpectraCat]

Thanks... initially that sounded great (get software to do it for me) so I took your advice. However, now it seems like it'd be quite a bit of overkill and a time-sink. I borrowed a copy of Spartan there and had a good play with it. It doesn't really appear designed for constructing bulk crystal structures, rather individual molecules (unlike for example VESTA). Nor could I find anything in the user guide that hinted at being able to create even a basic box and line MO energy-level diagram... it seems much more geared towards DFT and the like.

I think that would do me... I really just need to be able to draw or produce simple diagrams like this for TiO2: http://imgur.com/CfTfg

I was just wondering if you knew of any literature that guided one through those rules of thumb to generate such diagrams? (or if you knew more basic software that did a rough job of it?).

Ok, so it sounds like you actually want a band-structure diagram .. there are fewer software packages for calculating those .. at least *I* know of fewer packages. I also am not an expert in solid-state chemistry, which is really what you need to answer your question. You might consider cross-posting this to the Solid-state physics forum, or ask a moderator to move it for you. There are likely to be folks there who can help you with this in more detail.

Those line-diagrams are typically drawn after the fact as a way of visualizing the results of measurements or calculations, once you know the proper values for the various energy levels ... for a band structure diagram, you would have to know the appropriate energy ranges for the various bands as well. I suppose that you can draw an approximate version of you already know some qualitative information about the relative spacings of the atomic levels and the bands of the material. Do you know that information? I had gotten the impression that you were trying to use the diagram to estimate the properties of the material, so perhaps I misunderstood what you were asking.

Have you tried looking up band-structure diagrams in a solid-state physics or materials science text? That might be of more help than a chemistry text, which will generally restrict the presentation to molecular systems.

 

[cep]

I learned to draw orbitals from this book: https://www.amazon.com/dp/B003TYFQ1M/?tag=pfamazon01-20