Introduction


Preface	The VNL Toolbar

Virtual NanoLab (VNL) gives you access to a powerful set of modeling tools for investigating nanoscale structures through a user friendly graphical interface. The VNL software uses advanced software architecture and numerical methods to find solutions of the fundamental quantum mechanical equations describing the electronic properties of nanoscale objects, such as molecules, bulk and two-probe systems by use of the techniques

density functional theory (DFT)
non-equilibrium Green's functions (NEGF)

Based on the these techniques, VNL can simulate the detailed electronic structure and transport properties of molecules, crystals, nanotubes, and two-probe devices.

The way you work with VNL is in many aspects similar to what you would do in an actual experiment:

First you set up your system using either of the Molecular Builder, the Crystal Cupboard, or the Atomic Manipulator tools.
After setting up your system, you specify the details of the DFT method that should be applied to your system. You do this using either the Method Editor or the NanoLanguage Scripter tool.
Once the DFT method has been defined, you select the physical properties that should be extracted from the calculation. You do this by using the NanoLanguage Scripter tool.
The calculation is then performed by submitting the job to the Job Manager tool or executing it from the command line.
Finally, you analyze and inspect the obtained data by using the Nanoscope and the Result Browser tools.

In short, VNL is designed to bridge experimental and computational approaches by offering a spectrum of useful tools for performing virtual experiments. The NanoLanguage scripts that are generated with VNL are performed with the Atomistix ToolKit (ATK) calculation engine.

Since VNL is designed with ease-of-use in mind, you do not have to be an expert in quantum chemistry and electronic structure calculations to use it. Instead, you can focus on the physical properties of the systems under investigation, and let the program handle the details of the numerical models.

The numerical methods used in VNL are primarily based on first principles (ab initio) and do not, in principle, require any input parameters regarding the quantum-mechanical description of the atomic systems. Nevertheless, as is the case in most numerical simulations, a number of accuracy parameters must be specified to define the DFT and NEGF methods.

Even though detailed knowledge of the input parameters is essential for users who wish complete control of their calculations and results, non-expert users should certainly not feel intimidated by this requirement; only a small subset of the parameters are really important, and it is not difficult to understand how they work. The most relevant parameter settings are discussed in this tutorial, whereas more esoteric and complex parameters are described in detail in the VNL Manual.

	Note
	The Atomistix ToolKit (ATK) is the underlying engine performing all calculations in VNL. A complete description of all the parameters, and in many cases a longer discussion about their physical relevance, can be found in the ATK manual, which can be obtained as a PDF file from the Support section of the QuantumWise web site.

Finally, we are ready to begin the tour of Virtual NanoLab.