Timeline for Can orbitals in a molecule be occupied via excitation like they can in atomic orbitals?
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| Nov 13, 2017 at 11:56 | comment | added | Feodoran | If am not sure if I get your question right, but occupied orbitals can be quite intuitive, e.g. core orbitals which are al,pst identical to AOs, or bonding MOs where you can relate the number of nodes to the bonding character. These orbitals which are "generally shown in MO diagrams" do come somewhere from ;) However, virtual orbitals get more abstract and occasionally change with the AO basis set. Maybe this is worth a separate, new question ... | |
| Nov 13, 2017 at 9:44 | comment | added | Matthew John Jackman | I guess I would like to ask one more addition to what we are talking about, if you don't mind - do we know the defined shapes of these molecular orbitals like we do for, say, the ones generally shown in MO diagrams? Or is it a bit more abstract since we are talking about more complex mixtures of AOs? | |
| Nov 13, 2017 at 9:36 | vote | accept | Matthew John Jackman | ||
| Nov 13, 2017 at 8:33 | comment | added | Feodoran | Usually the cutoff includes all valence orbitals (or what you can form fram all valence AOs). Things like polarization functions are about the AO basis. But also influences the MOs, since you get as many MOs as AOs are supplied. Which also means FCI depends in the AO basis set. It can only consider as many MOs as are available. | |
| Nov 13, 2017 at 8:25 | comment | added | Matthew John Jackman | Thanks for the answer. In the case of virtual orbitals, would the 'cut-off' for 'important' orbitals tend to be set really only to those that aren't outside your typical molecular orbital diagram for that reason? I mean, of course excluding the addition of things like polarization basis sets and such. That is actually why I got the question actually - was reading about post-HF methods and was wondering about what they consider as the "full CI" if there are technically infinite states... guessing it must just be the 'important ones' i.e. valance electrons, maybe some rare Rydberg ones, yes? | |
| Nov 13, 2017 at 8:20 | history | answered | Feodoran | CC BY-SA 3.0 |