Van der Waals interactions in density- functional theory: implementation and applications

Aalto University, P.O. Box 11000, FI-00076 Aalto www.aalto.fi Author Andris Guļāns Name of the doctoral dissertation Van der Waals interactions in density-functional theory: implementation and applications Publisher School of Science Unit Applied Physics Series Aalto University publication series DOCTORAL DISSERTATIONS 6/2012 Field of research Electronic structure theory Manuscript submitted 3 October 2011 Manuscript revised 14 November 2011 Date of the defence 20 January 2012 Language English Monograph Article dissertation (summary + original articles) Abstract The density functional theory is, in principle, an exact ground-state method for interacting electrons. However, commonly applied local approximations make it severely unsuccessful for modelling materials where van der Waals interactions play a central role. The problem can be overcome by the van der Waals density-functional approach, which relies on a density functional with a built-in non-locality. This Thesis reflects on efforts towards efficient numerical implementation of the approach and its application to a variety of problems such as molecule adsorption, self-assembly and defects in graphite. Surprisingly for the condensed-matter community, in cases where a molecule is attached to a surface by the "weak" van der Waals forces they tend to be not so weak after all. These forces can seriously influence kinetics of various physical and chemical processes on surfaces or in layered solids. Hence, ignoring or mishandling the van der Waals interaction potentially leads to quantitatively and sometimes even qualitatively wrong results.The density functional theory is, in principle, an exact ground-state method for interacting electrons. However, commonly applied local approximations make it severely unsuccessful for modelling materials where van der Waals interactions play a central role. The problem can be overcome by the van der Waals density-functional approach, which relies on a density functional with a built-in non-locality. This Thesis reflects on efforts towards efficient numerical implementation of the approach and its application to a variety of problems such as molecule adsorption, self-assembly and defects in graphite. Surprisingly for the condensed-matter community, in cases where a molecule is attached to a surface by the "weak" van der Waals forces they tend to be not so weak after all. These forces can seriously influence kinetics of various physical and chemical processes on surfaces or in layered solids. Hence, ignoring or mishandling the van der Waals interaction potentially leads to quantitatively and sometimes even qualitatively wrong results.