Weak binding between two aromatic rings: feeling the van der Waals attraction by quantum Monte Carlo methods

Details Weak binding between two aromatic rings: feeling the van der Waals attraction by quantum Monte Carlo methods Weak binding between two aromatic rings: feeling the van der Waals attraction by quantum Monte Carlo methods

2007-02-15

arxiv.org/abs/cond-mat/0702349v1

Physics

Condensed Matter

Other Condensed Matter

12 pages, 6 figures, submitted to the Journal of Chemical Physics

Scientific paper

10.1063/1.2746035

We report a systematic study of the weak chemical bond between two benzene molecules. We first show that it is possible to obtain a very good description of the C_2 dimer and the benzene molecule, by using pseudopotentials for the chemically inert 1s electrons, and a resonating valence bond wave function as a variational ansatz, expanded on a relatively small Gaussian basis set. We employ an improved version of the stochastic reconfiguration technique to optimize the many-body wave function, which is the starting point for highly accurate simulations based on the lattice regularized diffusion Monte Carlo (LRDMC) method. This projection technique provides a rigorous variational upper bound for the total energy, even in the presence of pseudopotentials, and allows to improve systematically the accuracy of the trial wave function, which already yields a large fraction of the dynamical and non-dynamical electron correlation. We show that the energy dispersion of two benzene molecules in the parallel displaced geometry is significantly deeper than the face-to-face configuration. However, contrary to previous studies based on post Hartree-Fock methods, the binding energy remains weak (~ 2 kcal/mol) also in this geometry, and its value is in agreement with the most accurate and recent experimental findings.

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