Running the gamut of ab initio methods: application to questions of practical chemical interest
Brinkmann, Nicole Renee
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In pursuing a broad range of quantum chemical methods, a variety of ab initio methods have been used in application to questions of practical chemical interest. In the ﬁrst work included here, four commmon density functional or hybrid Hartree- Fock/density functional methods were used to study a newly-proposed mechanism of polymerization of methyl-2-cyanoacrylate (MCA) and ethyl-2-cyanoacrylate (ECA), two monomers frequently used in instant adhesives. The electron aﬃnities (EAs) of these two systems were predicted to be 1.08 eV. In comparison with previous work on cyano-substituted ethylenes, this value falls between the EA of cyanoethylene (0.06 eV) and 1,1-dicyanoethylene (1.36 eV). In the second study presented, high-level coupled-cluster theory was used with large basis sets to investigate the ground and ﬁrst three excited states of the methylene amidogen radical (CH2N) and its phosphorus analogue. Discrepancies with experimental results regarding ground state structures and energetic ordering of excited states were resolved. The excited states of CH2N are predicted to lie 33000 cm−1 ( ˜ A 2B1), 36000 cm−1 ( ˜B 2A ), and 38000 cm−1 ( ˜ C 2A1) above the ground state, and the excited states of CH2P to lie approximately 21000 cm−1 ( ˜ A 2A ), 26000 cm−1 ( ˜B 2B1), and 33000 cm−1 ( ˜ C 2A1) above the ground state. The last work presents a characterization of the ground and ﬁrst excited quartet states of the methylene cation (CH+2 ) using the coupled cluster method with singles, doubles, and perturbatively applied triples with Dunning’s correlation consistent polarized valence basis set series, core-valence basis sets, and augmented basis sets. The classical energy separation is predicted to be 86.9 kcal/mol, and the zero-point energy corrected value is 84.5 kcal/mol at the CCSD(T)/cc-pCVQZ level of theory.