I was coding a simple RHF code to test my understanding of computational chemistry when I stumbled upon this question. How exactly do computer programs like Gaussian, GAMESS-US etc. know which irreducible representation to assign to the molecular orbitals generated?
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asked Jul 23, 2019 at 12:11
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$\begingroup$ A molecule has a point group; a molecular orbital (or a group of MOs) has an irreducible representation. $\endgroup$– orthocresolCommented Jul 23, 2019 at 12:54
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$\begingroup$ The software constructs a symmetry adapted linear combinations (SALC) of the AOs. The IRREPs of the MOs follow directly from that: each MO is formed from SALCs of the same IRREP only. $\endgroup$– FeodoranCommented Jul 23, 2019 at 21:27
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1$\begingroup$ Thanks. How exactly does the software construct these SALCs? Projection Operator/Schmidt orthonormalisation? $\endgroup$– ANZGC FlyingFalconCommented Jul 24, 2019 at 11:24
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