Predicting both dispersion interactions and electronic structure using density functional theory

Noncovalent, dispersive interactions are essential to many fields of materials physics and chemistry. However, treatment of dispersion is inherently outside the reach of (semi)-local approximations to the exchange-correlation functional of density functional theory, as well as of conventional hybrid density functionals based on semi-local correlation. Here, we offer an approach that provides a treatment of both dispersive interactions and the electronic structure within a computationally tractable scheme. The approach is based on adding the leading interatomic dispersion term via pairwise ion-ion interactions to a suitably chosen non-empirical functional that is best suited for capturing the electronic structure, with the dispersion coefficients and van der Waals radii determined from first-principles using the recently proposed “TS-vdW” scheme. Here, we demonstrate the strength of this approach using two recent studies. In the first study, weakly bound metal-phthalocyanine dimers have been studied as a prototypical organic electronic system. We show that semi-local functionals can fail qualitatively, primarily because of under-binding of localized orbitals due to self-interaction errors. We find that the dispersion-corrected PBE-hybrid functional predicts both the electronic structure and the equilibrium geometry well. The performance of our approach is additionally compared to that of the semi-empirical M06 functional. The latter also predicts the electronic structure and the equilibrium geometry well, but with significant differences in binding energy and in asymptotic behavior compared to the dispersion-corrected PBE-hybrid functional. In the second study, the interlayer sliding energy landscape of hexagonal boron nitride (h-BN) was investigated using dispersion-corrected DFT calculations. We find that the main role of the van der Waals forces is to “anchor” the layers at a fixed distance, whereas the electrostatic forces dictate the optimal stacking mode and the interlayer sliding energy. A nearly free-sliding path is identified, along which bandgap modulations of 0.6 eV are obtained. We propose a simple geometrical model that quantifies the registry matching between the layers and captures the essence of the corrugated h-BN interlayer energy landscape. 1. A. Tkatchenko, M. Scheffler, Phys. Rev. Lett. 102, 073005 (2009). 2. N. Marom, A. Tkatchenko, M. Scheffler, and L. Kronik, J. Chem. Theo. Comp. 6, 81 (2010). 3. N. Marom and L. Kronik, Appl. Phys. A 95, 159 (2009); N. Marom, O. Hod, G. E. Scuseria, and L. Kronik, J. Chem. Phys. 128, 164107 (2008). 4. N. Marom, J. Bernstein, J. Garel, A. Tkatchenko, E. Joselevich, L. Kronik, and O. Hod, submitted.