Abstract:  Developments in mathematical methods and computational infrastructure have facilitated the solution of the Schrödinger equation for systems with multiple electrons and atoms. As a result, computational chemistry has become a convenient tool for investigating molecular geometries, chemical reactivity, spectrometry, biomolecules, and solids. Reactivity studies using computational chemistry rely on kinetic and dynamic theories, and several methods at its disposal are molecular mechanics, ab initio density functional theory, and molecular dynamics. The accuracy of each one of these methods varies, and a selection should consider the characteristic size and time scales of the molecular model under investigation.

The first objective of the Ph.D. research was to use transition state theory (TST) and several of its refinements to address uncertainties in the kinetics of butanol isomers, which are compounds comprehensively studied due to their compelling and general alcohol-based biofuel characteristics. The system-specific quantum Rice-Ramsperger-Kassel (SS-QRRK) theory is a viable alternative to estimate pressure effects since it only requires information about the reactant and the use of simple code. Besides, SS-QRRK incorporates TST refinements that other approaches do with considerable extra effort. However, its original formulation underestimates rate constants for C3 or larger systems at temperatures above 800 K. The second part of the Ph.D. research addressed this issue by testing two alternative collision efficiency definitions of the modified strong collision (MSC) model.