Weakly bonded systems

We are investigating ways to evaluate van der Waals interactions from first principles for simple systems, including molecular crystals, Self Assembled Monolayers (SAM) on surfaces and layered compounds. We use both Quantum Monte Carlo techniques and a so-called Exx/RPA approach, that combines exact exchange energies with correlation energies defined by the adiabatic connection fluctuation-dissipation theorem, within the random phase approximation (RPA).

Solid Benzenee
Binding curve of the van der Waals bonded benzene crystal as obtained using the Exx/RPA approach [1].

We have completed a study of intermolecular interactions in the benzene crystal [1]. Correlation energies are evaluated using an iterative procedure to compute the eigenvalues of dielectric matrices, which eliminates the computation of unoccupied electronic states [2-3]. Our results for the structural and binding properties of solid benzene are in very good agreement with experiment and show that the Exx/RPA framework is a very promising one to investigate molecular crystals and other condensed systems bound by dispersion forces. Work is in progress on solid methane and SAM on gold.

 

 

We have computed the binding energy of graphite layers in solid graphite by using Quantum Monte Carlo techniques [4].



References

  1. "Ab initio calculation of van der Waals bonded molecular crystals", D. Lu, Y. Li, D. Rocca and G. Galli, Phys. Rev. Lett., 102, 206411 (2009).
  2. "Efficient iterative methods for the calculation of dielectric matrices", H.Wilson, F.Gygi and G.Galli, Phys. Rev. B, 78,113303 (2008).
  3. "Iterative calculations of dielectric eigenvalue spectra", H.Wilson, D.Lu, F.Gygi and G.Galli, Phys. Rev.B, 79, 245106 (2009)
  4. “Nature and strength of interlayer binding in graphite”, L. Spanu, S.Sorella, G.Galli, Phys.Rev. Lett., 103, 196401 (2009).