Advances in Quantum Chemistry, Volume 86 highlights new advances in the field, with this new volume presenting topics covering Can orbital basis sets compete with explicitly correlated ones for few-electron systems?, Converging high-level equation-of-motion coupled-cluster energetics with the help of Monte Carlo and selected configuration interaction, Coupled cluster downfolding techniques: a review of existing applications in classical and quantum computing for chemical systems, Multi-reference methods for the description of dynamic and nondynamic electron correlation effects in atoms and molecules, Exploring the attosecond laser-driven electron dynamics in the hydrogen molecule with different TD-CI approaches, and much more. Additional sections cover Molecular systems in spatial confinement: variation of linear and nonlinear electrical response of molecules in the bond dissociation processes, Relativistic Infinite-order two-component methods for heavy elements, Second quantized approach to exchange energy revised – beyond the S^2 approximation, Calculating atomic states without the Born-Oppenheimer approximation,  Convergence of the Correlated Optimized Effective Potential Method, and more.