Overcoming three theoretical challenges in high accuracy ab initio electronic structure theory

Modern ab initio electronic theory provides an accurate method to compute molecular properties of subchemical accuracy. Despite recent advances and developments, many challenges arise that require special treatment for particular systems and properties. Here three theoretical challenges are addressed. First, the need of a high accuracy multireference method is discussed to properly describe radical-radical abstraction reactions in chemical combustion. Second, a warning is given against black-box computations by documenting anomalous imaginary frequencies in common planar and linear systems when post-Hartree-Fock methods are applied with insufficient basis sets. Third, an analysis is provided to quantify the qualitative concept of intramolecular dispersion by examining individual pair correlation energies.