ATK in Education: Crystals

Use ATK and VNL to study the electronic properties of crystals and other periodic structures. You can access the database of pre-built materials or build your own from scratch. Calculate basic properties such as the band structure with a few simple clicks. You can even compute and visualize Bloch functions!

By complementing the built-in functionality with custom-made NanoLanguage scripts, the students or their teacher can go beyond the basics and study for instance

• density of states
• supercells
• forces, stress, and the equation of state
• effective mass/curvature of bands in semiconductors
• dopant energy levels in semiconductors
• energy barriers for diffusion of dopants, using the transition state algorithm in ATK
• etc...

ATK in Education: Nanotubes & Graphene

Carbon nanotubes and graphene are ideal systems for demonstrating basic principles of both electronic structure and quantum transport. Their 1D and 2D structures provide foundations for discussions of k-point symmetries etc, and both electronic and transport characteristics can be compared to simple models. Both metallic and semiconducting behavior can be observed and discussed.

The structures are relatively cheap to calculate in ATK by using semi-empirical tight-binding models, and the results can then be compared to more general DFT calculations. Complex geometries, such as Stone-Wales defects or edge roughness in graphene nanoribbons, needs to be optimized first, and this can be done easily and extremely fast by the Brenner potential. See the movie to the right!

Nanotubes of any chirality, and endless variations on graphene nanoribbons can easily be built in VNL; see the figures below, as well as the page on graphene applications with ATK for more inspiration! Why limit yourself to carbon - it's just as easy to set up and calculate a boron-nitride or SiC tube, and for very interesting reasons they have quite different properties.

To get started on this topic in course-work, there are several prepared detailed tutorials on graphene that provide an excellent starting point. and thanks to the ways the GUI can be extended it is easy for a course instructor to provide the students with ready tools to create for specific structures. As an example, there is a plug-in tool which computes an analytic tight-binding band structure of carbon nanotubes. Then, the students can quickly set up the system and calculate the full DFT band structure (or use extended Hückel theory) with just a few mouse clicks and compare it to the simpler models. After that, introduce doping or defects to see how this influences the band structure - or the transport characteristics.

Another interesting exercise is to compute and visualize the Bloch functions in a nanotube or a graphene ribbon, with or without spin polarization, and relate its symmetries to the characteristic of each band (s-type, p-type, px vs pz, etc).

ATK in Education: Concepts of professional atomic-scale modeling

ATK is an ideal tool for demonstrating the principles of atomic-scale modeling in general, and transport studies in particular. The students can become acquainted with a professional atomic-scale modeling tool, and can get to grips with some of the fundamental challenges in the work-flow:

• Constructing a model for the problem at hand
• Setting up a corresponding geometry to represent the model
• Optimizing the structure, if needed
• Choosing a numerical model and the relevant parameters for it
• Post-processing and analysis; computing and visualizing observables
• Assessing the quality and reliability of the computed results

In addition, in advanced classes one can naturally introduce the students to the concepts of quantum transport calculations - the speciality of ATK!

• Make connections with simple models by looking at perfect nanotubes or linear metallic chains
• Introduce defects and study their influence on the transmission
• Go beyond the basics and study current-voltage characteristics of molecular electronic systems, tunnel-magnetoresistance in magnetic tunnel junctions, rectification in graphene nanoribbons
• And much more!

Moreover, Python is become a very popular language within physics and chemistry. By inspecting the input scripts the students can quickly learn the basic syntax and semantics of Python, and get started developing more advanced geometry setups and analysis functions.

Working with ATK also provides a simple way to go beyond the basic toy models in the teaching of fundamental quantum mechanics, and instead study realistic atomic systems. Moreover, there are ample chances for discussion in class the basic concepts of density-functional theory, and how these may influence the quality and reliability of the results.