Research interests in our research group

The main focus of this group is to study quantum non-equilibrium systems and to develop the underlying theoretical tools and methods. The main approaches to non-equilibrium physics are Time-Dependent Density Functional Theory (TDDFT) and Nonequilibrium Green's Function theory (NEGF). As an application the Green's function method is applied to describe quantum transport through molecular devices.

What is quantum many-body theory?

All objects we see around us everyday are made up of electrons and atomic nuclei. Questions about the nature of these objects, such as their color, the question whether the object is a solid, liquid or a gas, or whether it may be superconducting or ferromagnetic are ultimately questions about the quantum mechanical behavior of systems made up of electrons and atomic nuclei. These systems may not be in a stationary state. They may, for instance, be excited by lasers or carry electronic currents and therefore be in a dynamical state. To describe such phenomena we need a dynamical description of quantum many-particle systems. In principle we know the quantum mechanical laws that describe the dynamical evolution of these systems. To predict the properties of such systems we simply need to solve the time-dependent Schrödinger equation. The problem is that this is not possible in practice. First of all, in the range from atoms and molecules to solids we are dealing with systems with an electron number (and the same for nuclei) ranging from 1 to 1023. Which means that we are dealing with quantum mechanical wave functions of an enormous number of variables. Secondly, all these particles are interacting with Coulombic forces such that the motion of the particles are not independent and therefore equations can not be simplified. We are therefore faced with the question how to theoretically predict properties of such systems. This problem is commonly known as the many-body problem. It is a central problem in theoretical physics and an enormous amount of work has been done to attack this problem. One key observation is that most experimental properties of many-particle systems involve one and two-body observables such as densities and currents, polarizabilities, spin quantum numbers, pair correlation functions etc. This suggests that it may be possible to describe the properties of many-body systems in terms of reduced quantities, i.e. quantities that are obtained by integrating out all but a few of the variables of the many-body wave function. This idea has turned out to be very fruitful and has led to various theoretical approaches to attack the many-body problem. These approaches are nonequilibrium Green's function theory, density functional theory and density matrix theory. In our research group all these three approaches are developed and applied to the study of many-particle systems.

Selected publications

Publication 1

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Publication 2

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Publication 3

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