The full Coulomb interactions, i.e., electron-electron and electron-impurity interactions, play an important role in the operation of ultra-small MOSFETs. Previous simulation approaches (particle-mesh and particle-particle/particle-mesh methods) were found to be very time-consuming because of the imposed boundary conditions. We used a fast multi-pole method instead and verified its applicability in bulk mobility and device simulations. This approach yields physically correct results and accounts for all Coulomb interactions in the device within significantly decreased simulation times.
Another aim was to incorporate quantum mechanical corrections into a particle-based Monte Carlo semiconductor device simulator by replacing the classical forces acting on the electrons during free flight by modified quantum mechanical forces. We have been extending the use of an effective quantum potential to particle-particle interactions. This means that the electron-barrier interactions and, additionally, the electron-electron interactions can now be handled including the quantum mechanical correction. The effective quantum potential was derived for the many-body problem and recently implemented in our three-dimensional Monte Carlo simulator.
A new and exciting area of research, where methods for many-body problems play a significant role, is molecular biotechnology. For a long time after the Nobel prize-winning works of Hodgkin and Huxley on the chemical processes responsible for the passage of impulses along neurons, the precise mechanism underlying ion channels and ion transporters remained a mystery. The mechanisms of selective ion conduction, i.e., why only certain ions can pass an ion channel, and gating, i.e., how ion conduction is turned on and off depending on specific environmental stimuli, are fundamental to cell biology. The selectivity mechanism of potassium channels on the atomic level was first explained by the X-ray diffraction experiments performed in MacKinnon's group. MacKinnon and Agre shared the 2003 Nobel prize in chemistry for their work on potassium and aquaporin water channels, respectively. The mechanism of gating in ion channels, however, is not yet fully understood. The number of membrane proteins whose atomic structure is known has increased fast recently, and this is stimulating research. The corresponding molecular dynamics simulations, important for our theoretical understanding as well as for computer-aided drug design, are very computationally expensive and among the most demanding scientific computations. We simulate the workings of ion channels on the atomic level in order to explain their functioning and in order to use this knowledge in computer-aided drug design.