Non-covalent van der Waals (vdW) forces are crucial for the formation,
stability and function of molecules and materials. At present,
ubiquitous vdW interactions can only be accounted for properly by
high-level quantum-chemical wave function or by the Quantum Monte
Carlo (QMC) method. In contrast, the correct long-range interaction
tail, e.g., for separated molecules, is absent from all popular
local-density or gradient corrected exchange-correlation functionals
of density-functional theory. We have recently developed an efficient
method to obtain accurate vdW dispersion coefficients from first
principles [1]. This method can be coupled to DFT calculations and
even to quantum-chemical MP2 approach [2]. I will discuss the
theoretical underpinnings of the method and applications to different
cases: intermolecular and intramolecular interactions [1,2],
organic/organic interfaces [3], organic/inorganic interfaces [4,5] and
cohesive properties of ionic and semiconductor solids.

[1] A. Tkatchenko and M. Scheffler, Phys. Rev. Lett. 102, 073005 (2009).
[2] A. Tkatchenko, R. A. DiStasio Jr., M. Head-Gordon and M.
Scheffler, J. Chem. Phys. 131, 094106 (2009).
[3] N. Marom, A. Tkatchenko, M. Scheffler and L. Kronik, J. Chem.
Theory Comp. 6, 81 (2010).
[4] E. McNellis, J. Meyer, and K. Reuter, Phys. Rev. B 80, 205414 (2009).
[5] G. Mercurio et al., Phys. Rev. Lett. 104, 036102 (2010).