Dynamic quantum mechanical simulations of materials at multiple scales

The study of our physical environment through quantum mechanical (QM) calculations of the electron structures of materials and molecules is an ever-growing area of research. Electron structure calculations have proven to be useful in many sciences; from solid state physics to pharmacology. They have not only increased the understanding of experimental results but have also shown that they can predict important properties and thus enable the rational design of molecules and materials on the basis of these theoretical predictions. Calculations of electronic structures have even established themselves in biology, the science of life itself. With this increased scientific understanding and possible applications to challenges in areas such as medicine and nanotechnology, electronic structure calculations have a huge potential impact, even on the everyday world around us.

The scope of electronic structure calculations is further extended in quantum or ab-initio molecular dynamics (QMD/AI-MD), where the entire dynamics of the system, the motions of atoms, at realistic temperatures are simulated. One of the most important theoretical techniques for studying large systems at room temperature, important for e.g. biological or polymeric systems, is so-called molecular dynamics (MD) simulations. In MD, the system is described as a set of particles moving according to the laws of classical mechanics over a given potential energy surface. Depending on how the interactions between the particles are obtained, MD methods can be divided into classical force field MD methods or quantum mechanical MD methods. Although classical force-field MD methods, which are by far the most widely used method, are very successful for the simulation of many biological and polymeric systems, chemical reactions and more complex atoms, e.g. transition metals, can only be satisfactorily treated using a full quantum mechanical description. In quantum mechanical MD (QMD) methods, all interactions are calculated from an electron structure method (here density functional theory – DFT). QMD simulations are therefore parameter-free and allow a direct and potentially unbiased simulation of chemical and physical events. Since the temperature of the systems is taken into account, a selection of the conformational space, possible geometries, is made, which also means that the simulations are less influenced by the choice of, for example, initial conditions and selected reaction coordinates.

Thermoelectric polymers

To meet the increasing demand for electricity in the world (estimated to double to 26 TW by 2050), we are constantly looking for alternative renewable energy sources that can be converted into electricity. Since the sun is the largest available energy source, which could easily meet our energy needs with a radiant power in the order of 100 000 TW, converting solar energy into electricity is very appealing. One of the most promising ways to convert solar heat into electricity is to use thermoelectric generators (TEGs). TEGs are constructed using thermoelectric materials, materials in which a difference in temperature causes an electric current to flow through the materials, the so-called Seebeck effect. The disadvantages of the inorganic thermoelectric materials currently in use are that they consist of toxic elements with low natural abundance. Organic polymer-based thermoelectric materials, on the other hand, while currently less efficient, can be mass-produced using safer, highly abundant elements at low cost.