Henrik Rydberg

Van der Waals density functional for general geometries

A scheme within density functional theory is proposed that provides a practical way to generalize to unrestricted geometries the method applied with some success to layered geometries [Phys. Rev. Lett. 91, 126402 (2003)]]. It includes van der Waals forces in a seamless fashion. By expansion to second order in a carefully chosen quantity contained in the long-range part of the correlation functional, the nonlocal correlations are expressed in terms of a density-density interaction formula. It contains a relatively simple parametrized kernel, with parameters determined by the local density and its gradient. The proposed functional is applied to rare gas and benzene dimers, where it is shown to give a realistic description.

Van der Waals density functional for layered structures.

To understand sparse systems, we must account for both strong local atom bonds and weak nonlocal van der Waals forces between atoms separated by empty space. A fully nonlocal functional form [Phys. Rev. B 62, 6997 (2000)]] of density-functional theory (DFT) is applied here to the layered systems graphite, boron nitride, and molybdenum sulfide to compute bond lengths, binding energies, and compressibilities. These key examples show that the DFT with the generalized-gradient approximation does not apply for calculating properties of sparse matter, while use of the fully nonlocal version appears to be one way to proceed.

Tractable nonlocal correlation density functionals for flat surfaces and slabs

A systematic approach for the construction of a density functional for van der Waals interactions that also accounts for saturation effects is described, i.e. one that is applicable at short distances. A very efficient method to calculate the resulting expressions in the case of flat surfaces, a method leading to an order reduction in computational complexity, is presented. Results for the interaction of two parallel jellium slabs are shown to agree with those of a recent RPA calculation (J.F. Dobson and J. Wang, Phys. Rev. Lett. 82, 2123 1999). The method is easy to use; its input consists of the electron density of the system, and we show that it can be successfully approximated by the electron densities of the interacting fragments. Results for the surface correlation energy of jellium compare very well with those of other studies. The correlation-interaction energy between two parallel jellia is calculated for all separations d, and substantial saturation effects are predicted.

Unified treatment of asymptotic van der Waals forces

In a framework for long-range density-functional theory we present a unified full-field treatment of the asymptotic van der Waals interaction for atoms, molecules, surfaces, and other objects. The only input needed consists of the electron densities of the interacting fragments and the static polarizability or the static image plane, which can be easily evaluated in a ground-state density-functional calculation for each fragment. Results for separated atoms, molecules, and for atoms/molecules outside surfaces are in agreement with those of other, more elaborate, calculations.

Hard numbers on soft matter

Graphitic systems are ideal examples of the soft-matter challenge for quantum mechanics that must account for both strong local atom bonds and weak nonlocal van der Waals interactions between atoms separated by empty space. Here a new density functional (DF), which encompasses nonlocal correlations among the electrons, is applied successfully to obtain structure, bonding, and compressibility, documenting the decisive role of the interlayer vdW interactions. The understanding emerging from this new extended-DF formulation has bearing on broad classes of problems, including surfaces, in physics, chemistry, biology, medicine, and technology, where we can now provide an efficient and accurate DF-theory account.

Density-functional bridge between surfaces and interfaces

Interfaces are brought into focus by many materials phenomena, e.g., contacting, materials strength, and wetting. The class of interfaces includes ultra-high-vacuum surfaces, which provide a meeting place for numerous accurate experimental techniques and advanced theory. Such meetings stimulate detailed comparisons on the quantum level between experiment and theory, which develop our theoretical tools and understanding. This creates good positions for broadened applications, e.g., other interfaces, which typically lack adequate experimental tools. Density-functional theory is one key bridge between surfaces and other interfaces. The paper presents some recent typical applications from our group, including brief reports on interface structures (VN/Fe, TiC/Co, TiC/Al 2 O 3 ), dynamic processes at surfaces and interfaces (O 2 /Al(111), scanning-tunneling microscopic spectroscopy and manipulation), adsorption and desorption (CO, N 2 , NO, and O 2 on Al(111)), electronic and magnetic properties at surfaces and interfaces (magnetic effects on TiC/Co, surface state on κ-Al 2 O 3 (001)), and epitaxial growth on surfaces (Al(111) and alike). Similar progress in many worldwide materials groups and networks gives a basis for the ongoing paradigm shift in materials science.

Density functionals and van der Waals interactions at surfaces

Abstract Recent progress in the construction of a density functional for van der Waals interactions is described, towards the background of successes of local and semi-local exchange-correlation density functionals for dense matter. The functional should apply for atoms, molecules, surfaces, and other objects. The only input needed consists of the electron densities of the interacting fragments or surfaces, and their static polarizabilities or static image planes, respectively, which can be easily evaluated in a ground-state density-functional calculation. Results for well separated atoms, molecules, and atoms/molecules outside surfaces are in agreement with those of other, more elaborate, calculations. A description of the asymptotic van der Waals interaction between two parallel surfaces is also given.