Electronic Spec - Terms generated by config of (e1g)2(e2u)2

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SUMMARY

The discussion focuses on the terms generated by the configuration (e1g)²(e2u)² in D6h symmetry. The correct terms derived from the direct product calculations are 31A1g + 3A1g + 5A1g + 1A2g + 23A2g + 31E2g + 23E2g. The initial calculations contained errors in the application of the direct product rules, particularly in the interpretation of singlet and triplet combinations. Clarifications were provided to correct the miscalculations and ensure accurate term generation.

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  • Understanding of D6h symmetry in group theory
  • Familiarity with direct product calculations in quantum mechanics
  • Knowledge of singlet, doublet, triplet, and quartets in terms of quantum states
  • Experience with symmetry-adapted linear combinations of atomic orbitals (SALCs)
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  • Study the application of direct product rules in group theory
  • Learn about symmetry operations in molecular orbital theory
  • Explore the concept of symmetry-adapted linear combinations (SALCs) in quantum chemistry
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This discussion is beneficial for theoretical chemists, physicists, and students studying molecular symmetry and quantum mechanics, particularly those interested in the application of group theory to molecular orbital theory.

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Homework Statement


What terms are generated by the configuration (e1g)2(e2u)2 in D6h symmetry?

Homework Equations


configuration (χd)2 gives terms 1(symmetric product) + 3(antisymmetric product) where χ=symmetry of an orbital and d = degenerate

(e1g)x(e1g) = A1g + [A2g] + E2g
(e2u)x(e2u) = A1g + [A2g] + E2g
where brackets [ ] indicate antisymmetric product

s=singlet, d=doublet, t=triplet, q=quartet, qu=quintet
sxs = s
sxd = d
sxt = t
sxq = q
dxd = s + t
dxt = d+q
dxq = t+qu
txt = s+t+qu
txq = d+q+sextet
qxq = s+t+qu +septet

The Attempt at a Solution


So first I found the terms generated by e1gxe1g and e2uxe2u separately
(e1g)2x(e1g)2 = 1A1g + 3A2g + 1E2g
(e2u)2x(e2u)2 = 1A1g + 3A2g + 1E2g

Then find direct product of [(e1g)x(e1g)]x[(e2u)x(e2u)]
1A1g 1A1g
3A2g x 3A2g =
1E2g 1E2g

1A1gx1A1g + 1A1gx3A2g + 1A1gx 1E2g
3A2gx1A1g + 3A2gx3A2g + 3A2gx 1E2g =
1E2gx1A1g + 1E2gx3A2g + 1E2gx 1E2g

1A1g + 3A1g + 2A2g + 4A2g + 2E2g
1A1g + 3A1g + 5A1g + 2A2g + 4A2g + 3E2g
1A1g + 1A2g + 1E2g + 2E2g + 3E2g

= 31A1g + 23A1g + 5A1g +1A2g +22A2g +24A2g + 1E2g + 22E2g + 23E2g

The correct answer is
31A1g + 3A1g + 5A1g +1A2g +23A2g + 31E2g + 23E2g

I assume I'm messing up in when doing this direct product: [(e1g)x(e1g)]x[(e2u)x(e2u)].
but I'm not sure exactly what I'm doing wrong. Any help is really appreciated!
 
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You messed some things up: This is probably a typo:
"So first I found the terms generated by e1gxe1g and e2uxe2u separately
(e1g)2x(e1g)2 = 1A1g + 3A2g + 1E2g
(e2u)2x(e2u)2 = 1A1g + 3A2g + 1E2g" and should read
"So first I found the terms generated by e1gxe1g and e2uxe2u separately
(e1g)x(e1g) = 1A1g + 3A2g + 1E2g
(e2u)x(e2u) = 1A1g + 3A2g + 1E2g"

Then a singlet times a triplet does not give a quartett:
1A1gx3A2g is not 4A2g but 3A2g.
Similarly 1A1gx 1E2g is not 2E2g but 1E2g. There are more of this kind.
It would be helpful if you could write down for each term in the sum how it is reduced out.
E.g. 1A1gx1A1g=1A1g, ...
 

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