Ab-Initio-Based Potential Energy Surfaces for Complex Molecules and Molecular Complexes

The Born−Oppenheimer potential energy surface(s) underlies theoretical and computational chemistry (whether one considers a single or multiply coupled surfaces). The recent progress in representing these surfaces, rigorously obtained from electronic structure calculations, is the focus of this Perspective. Examples of potentials of complex molecules, namely, CH 3 CHO, CH 5 +, and H 5 +, and molecular complexes, namely, water clusters, are given.