WFU Physics Colloquium

TITLE: Multiscale Modeling in Computational Condensed Matter Physics: From Small Atomic Clusters to Semiconductor Wafers

SPEAKER: Dr. Christian Ratsch,

TIME: Monday Feb. 9, 2009 at 4:00 PM

PLACE: Room 101 in Olin Physical Laboratory

Physical processes for many problems in condensed matter physics and materials sciences span length and time scales of many orders of magnitude. For example, on the microscopic level, atoms move several Ångstroms (the lattice constant), and vibrate with a frequency of approx. 10¹³ 1/s. On the other hand, phenomena and applications of practical interest occur on a timescale of seconds, with system sizes that can be microns or larger. The grand challenge in computational condensed matter physics is to link those vastly different time and length scales. In this talk, I will discuss several examples where different theoretical techniques have been used. These techniques are valid on different time and length scales and are in fact complementary to each other, to form a hierarchy of models.

As a first example, I will discuss how density-functional theory (DFT) in conjunction with experimental data can be used to determine the detailed atomistic structure and vibrational properties of small metal clusters. Such clusters play a key role in many technologically relevant applications, such as catalysis. In a second example, I will focus on the description of epitaxial growth. A particular challenge is modeling epitaxial growth is the inclusion of strain, that arises when different materials (with different lattice constants) are involved, such as growth of the GeSi or InGaAs systems. We model epitaxial growth with an island dynamics model that utilizes the level-set method to describe the formation of islands and the evolution of their boundaries. Our model is ideally suited to be combined with an elastic model. DFT calculations can be used to parameterize the strain dependence of the relevant growth parameters. Finally, strain induced ordering of islands and quantum dots, and the formation of stacked quantum dots will be discussed.