Pushing the ab initio limits for the accurate characterization of small molecular systems
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Modern quantum chemistry has merged as one of the most important tools for understanding and predicting various properties of chemical systems. Highly accurate <i>ab initio</i> methods like CCSD(T) provide quantitative theoretical predictions that can be used to assist or even guide the experiments. Herein, state-of-the-art <i>ab initio</i> methods are applied on two small molecular systems. In the characterization of the simplest metal carbene, BeCH<sub>2</sub>, energetic properties are investigated employing coupled cluster methods up to CCSDTQ and extrapolated to complete basis set limit using focal point analysis (FPA). Additionally, states with strong multi-reference characters are studied using MRCISD method with large basis sets. In another study, the reactions involved in the formation of BH<sub>2</sub>6<sup>+</sup> are investigated exhaustively. H<sub>2</sub> binding energies determined using FPA agree perfectly with experiments. Furthermore, the previous discrepancy on activation energies is essentially solved by computing the insertion reaction rates with tunneling effects.