title: Spooky correlations and unusual van der Waals forces between gapless and near-gapless molecules.
abstract: We consider the zero-temperature van der Waals (vdW) interaction between two molecules, each of which has a zero or near-zero electronic gap between a ground state and the first excited state, using a toy model molecule (equilateral H3) as an example. We show that the van der Waals energy between two ground state molecules falls off as D-3instead of the usual D-6dependence, when the molecules are separated by distance D. We show that this is caused by a perfect "spooky" correlation between the two fluctuating electric dipoles. The phenomenon is related to, but not the same as, the "resonant" interaction between an electronically excited and a ground state molecule introduced by Eisenschitz and London in 1930. It is also an example of "type C van der Waals non-additivity" recently introduced by one of us [J. F. Dobson, Int. J. Quantum Chem. 114, 1157 (2014)]. Our toy molecule H3is not stable, but symmetry considerations suggest that a similar vdW phenomenon may be observable, despite Jahn-Teller effects, in molecules with a discrete rotational symmetry and broken inversion symmetry, such as certain metal atom clusters. The motion of the nuclei will need to be included for a definitive analysis of such cases, however.
authors.affiliation: School of Natural Sciences and Queensland Micro and Nano Technology Centre, Griffith University, Nathan, Queensland 4111, Australia.
authors.forename: John F
authors.initials: JF
authors.lastname: Dobson
authors.affiliation: UPMC Sorbonne Universités, Laboratoire de Chimie Théorique, 4 Place Jussieu, Case Courrier 137, F-75252 Cedex 05 Paris, France.
authors.forename: Andreas
authors.initials: A
authors.lastname: Savin
authors.affiliation: Laboratoire de Cristallographie, Résonance Magnétique et Modélisations (CRM2, UMR CNRS 7036) and Institut Jean Barriol, Université de Lorraine, BP 239, Boulevard des Aiguillettes, 54506 Vandoeuvre-lès-Nancy, France.
authors.forename: János G
authors.initials: JG
authors.lastname: Ángyán
authors.affiliation: Institut Jean Barriol, Université de Lorraine, BP 239, Boulevard des Aiguillettes, 54506 Vandoeuvre-lès-Nancy, France.
authors.forename: Ru-Fen
authors.initials: RF
authors.lastname: Liu