title: Investigating Disjoint Non-Kekulé Diradicals with Quantum Monte Carlo: The Tetramethyleneethane Molecule through the Jastrow Antisymmetrized Geminal Power Wave Function.
abstract: Disjoint non-Kekulé molecules are diradicals that present two independent radical centers and can violate Hund's rule, according to which the ground state should have triplet spin symmetry. The prototype of this class of systems is the tetramethyleneethane (TME) molecule for which indeed ion photoelectron spectroscopy (IPS) experiments revealed the singlet (1)A state to be more stable than the triplet (3)Bu. In this work we investigate the potential energy curves of the two spin states of TME and of the two anionic states of TME(-) ((2)A and (2)B1) as a function of the torsion of the central dihedral angle, with quantum Monte Carlo methods and a Jastrow Antisymmetrized Geminal Power wave function. Through ab initio geometrical optimizations we study the possible structural interconversions between the states, finding results which are in full agreement with the IPS experimental data.
authors.affiliation: S3 Research Center, CNR-NANO , Via Campi 213/a, 41125 Modena, Modena, Italy.
authors.forename: Matteo
authors.initials: M
authors.lastname: Barborini
authors.affiliation: Laboratoire de Chimie Théorique, Sorbonne Universités, UPMC Univ Paris 06 & CNRS, UMR 7616 , F-75005 Paris, France.
authors.forename: Emanuele
authors.initials: E
authors.lastname: Coccia