Multicomponent Quantum Chemistry: Integrating Electronic and Nuclear Quantum Effects
Sharon Hammes-Schiffer
Department of Chemistry, Yale University, New Haven, CT 06520
Nuclear quantum effects such as zero point energy, nuclear delocalization, and tunneling play an important role in a wide range of chemical processes. Typically quantum chemistry calculations invoke the Born-Oppenheimer approximation and include nuclear quantum effects as corrections following geometry optimizations. The nuclear-electronic orbital (NEO) approach treats select nuclei, typically protons, quantum mechanically on the same level as the electrons with multicomponent density functional theory (DFT) or wavefunction methods. Recently electron-proton correlation functionals have been developed to address the significant challenge within NEO-DFT of producing accurate proton densities and energies. Moreover, delta self consistent-field methods and timedependent DFT methods within the NEO framework have been developed for the calculation of electronic, proton vibrational, and electron-proton vibronic excitations. Multicomponent wavefunction methods based on coupled cluster and configuration interaction approaches have also been developed within the NEO framework. These combined NEO methods enable the inclusion of nuclear quantum effects and non-BornOppenheimer effects in calculations of proton affinities, pKa’s, optimized geometries, vibrational frequencies, isotope effects, minimum energy paths, reaction dynamics, excitation energies, tunneling splittings, and vibronic couplings for a wide range of chemical applications