Exchange-correlation functionals in solids

01.01.2008 - 31.12.2010
Research funding project
Nowadays, the Kohn-Sham version of density functional theory is the most used theoretical method to study the electronic structure of molecules, surfaces, and solids. Unfortunately the exact analytical expression for the exchange-correlation energy functional is unknown, therefore only approximations can be used. The reliability of any Kohn-Sham calculation depends i) on the numerical accuracy when solving these equations and ii) on the approximation used for the exchange-correlation energy. For the solution of the Kohn-Sham equations we use the WIEN2k code, which utilizes a flexible all-electron (L)APW+lo basis set and represents one of the most accurate methods for solid state computations. It is used by more than 1100 groups worldwide. On the other hand this explains why the search for more accurate approximations for the exchange-correlation is an intensive research area both in chemistry and physics. The development, implementation, and testing of exchange-correlation functionals constitute the main topics of this research proposal. More specifically, we plan to implement the (screened) Hartree-Fock method into the WIEN2k code in order to have the possibility to apply hybrid functionals on periodic solids. The last years have seen the emergence of hybrid functionals for solids and it has been shown that hybrid functionals yield very accurate results for various properties (e.g., geometry and structure) of different types of compounds (e.g., semiconductors and strongly correlated systems), in many cases outperforming the standard LDA and GGA approximations for the exchange-correlation energy. Another part of the project will consist of the development of more accurate exchange-correlation functionals of the GGA or meta-GGA type. The GGA functionals in particular (e.g., PBE) are still the most used functionals for solid-state calculations, and one of the main reasons for that is that they are easy to implement and computationally cheap. Several recent publications have shown that this type of approximations can still be improved. An in-depth analysis of the performance of GGA functionals will also be done in order to understand why a given GGA functional works for a given class of elements (or compounds) but not for another. Finally, non-covalent interactions will also be studied. It is well known that the correct description of non-covalent interactions constitutes one of the most difficult challenges for the Kohn-Sham method. Different types of functionals especially designed for non-covalent interactions were proposed in the literature. Some of these functionals are ¿fully non-local¿ while others have a simple (but empirical) form. A literature survey of this topic shows that a large part of these works on improved functionals for non-covalent interactions concerns mainly molecules, while for solids such works are rather scarce. We plan to implement such functionals into the WIEN2k code and to test them on solids for which non-covalent interactions play an important role.

People

Project leader

Project personnel

Institute

Grant funds

  • FWF - Österr. Wissenschaftsfonds (National) Austrian Science Fund (FWF)

Research focus

  • Non-metallic Materials: 5%
  • Quantum Modeling and Simulation: 80%
  • Computational Materials Science: 10%
  • Materials Characterization: 5%

Keywords

GermanEnglish
DichtefunktionaltheorieDensity Functional Theory
Hartree-FockHartree-Fock
Hybrid-FunktionaleHybrid-Functionals
WIEN2kWIEN2k

Publications