An Assessment of the vdW-TS Method for Extended Systems

Abstract

The Tkatchenko-Scheffler vdW-TS method [Phys. Rev. Lett.2009, 102, 073005] has been implemented in a plane-wave DFT code and used to characterize several dispersion-dominated systems, including layered materials, noble-gas solids, and molecular crystals. Full optimizations of the structures, including relaxation of the stresses on the unit cells, were carried out. Internal geometrical parameters, lattice constants, bulk moduli, and cohesive energies are reported and compared to experimental results.

Understanding the role of vibrations, exact exchange, and many-body van der Waals interactions in the cohesive properties of molecular crystals

“…Compared to PBE, which is known to often substantially overestimate lattice constants, 29 both the pairwise and many-body approaches give good agreement with experiment, with many of the differences likely to be of the order of zero-point and thermal vibrational contributions to the lattice constants. The estimation of these contributions for any crystal is non-trivial and will form part of our future work in this area.…”

“…Hybrid functionals are often not used in the study of cohesive properties of molecular crystals, 29,30 largely due to their additional computational cost, which particularly in a plane-wave basis can reach more than an order of magnitude larger than the corresponding semi-local functional. The present database of crystals suggests that hybrids may be important for accurate work.…”

“…Compared to PBE without any vdW contributions, PBE+TS yields very good lattice parameters, often within a few percent of experimental values. 29,30 To understand the role of MBD in determining the structure of molecular crystals, the lattice parameters and internal geometries of a selection of molecular crystals have been optimized at the PBE+MBD level. The resulting lattice parameters are compared with PBE+TS and experiment in Table VII.…”

“…It is equally important to properly assess the role of the density functional used to calculate the lattice energies. While many studies have focused on the role of dispersion, 25,29,30 few have critically assessed the shortcomings of semi-local functionals in detail. For example, the de-localisation or selfinteraction errors in DFT 31 can often have a significant effect on hydrogen-bonded systems.…”

Communication: Accurate higher-order van der Waals coefficients between molecules from a model dynamic multipole polarizability

“…As a result, it often fails to describe the intermolecular interaction and phenomena arising from it (e.g., sublimation and physisorption). It has been shown that a proper vdW correction can significantly improve the performance of conventional DFT, greatly extending its applicability to a broader class of problems such as molecular complexes and solids [2][3][4][5][6][7][8][9] and layered materials. 10,11 The vdW interaction is an important long-range nonlocal correlation arising from instantaneous charge fluctuations on each density fragment.…”