Theory of Intermolecular Forces: an Introductory Account

Modern theory of intermolecular forces is reviewed. The concept of the interaction potential is introduced within the Born-Oppenheimer separation of the electronic and nuclear motions. Various supermolecule approaches for the calculation of accurate interaction potentials are discussed. Perturbation theory of intermolecular forces is reviewed in great details. The problem of symmetry-adaptation is explained and a general symmetry-adapted perturbation theory is formulated. Convergence properties of various symmetry-adapted expansions are surveyed, and illustrated on several examples. Physical interpretation of the interaction potential in terms of the four fundamental interaction components: electrostatics, induction, dispersion, and exchange-repulsion is thoroughly exposed. Many-electron formulation of the symmetry-adapted perturbation theory in both the wave function and density functional approaches is introduced. One-center and multicenter multipole expansions neglecting the charge-overlap effects, as well as the bipolar expansion accounting for these effects are discussed. The relation of some supermolecule approaches with the perturbation theory of intermolecular forces is briefly sketched. Approximate models that can be deduced from the rigorous theory of intermolecular forces, and applicable to the interactions of large systems are discussed. Finally, perturbation theory of nonadditive interactions in trimers and of the collision-induced electric properties of binary collisional complexes is also reviewed. The theory part is completed by an exposition of methods needed on the route from intermolecular potentials and collision-induced properties to physically measurable quantities such as the Raman spectra, rovibrational spectra, scattering cross sections, as well as thermodynamic, dielectric, and refractive properties of dilute gases. The present status of symmetry-adapted perturbation theory applied to the calculations of state-of-the-art

ab initio

potential energy surfaces and collision-induced properties is presented, and illustrated by means of applications to rovibrational spectra of Van der Waals molecules, scattering cross sections and pressure broadening coefficients, collision-induced Raman spectra of atomic gases, solvation processes, and thermodynamic, dielectric, and refractive properties of dilute gases. Theoretical results are compared with high accuracy experimental data