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New release: Atomistix ToolKit Semi-Empirical (ATK-SE) 2009.06

ATK-SE sets a new standard for nanoscale device simulations! Faster than DFT, allowing for larger systems, and featuring a unique capability to calculate how electrostatic (metallic and dielectric) gates influence the electron transport. And that's just the beginning...! 


QuantumWise is proud to announce the release of its new software package for simulations of electronic structure and transport properties of nanostructures, Atomistix ToolKit Semi-Empirical (ATK-SE). ATK-SE offers basically the same functionality as ATK-DFT, while at the same time introducing several new features that allow for even more realistic modeling of nanoscale electronic devices.

 

To download the new release, please go to the Download page.

 


See below for detailed information on

 

Main new features and advantages

Faster calculations

Even relatively complex calculations, like a current/voltage curve of a graphene nanoribbon transistor, can be completed in hours, rather than days as with DFT.

Right: The transmission spectrum of a graphene nanowire under bias, computed with ATK-SE and set up and computed in VNL 2009.06.

 

Graphene nanowire transmission spectrum

Realistic simulation of transistor structures

In the new electrostatic model introduced in ATK 2009.06, you can include any number, shape, and configuration of gates, both dielectric and metallic. The gates are described fully self-consistently electrostatically, which allows for a realistic simulation of transistor-like structures. The gates are treated as continuous regions, while the transport system is described fully atomistically, and thus this is the first step in the development of next-generation multi-scale models of nanoscale device structures.

Right: The geometry of the graphene nanoribbon device visualized with VNL. Within the central region there is a dielectric region (brown transparent region) and below this a metallic electrostatic gate (light blue). The contour plot shows the electrostatic potential for a gate potential of 1 Volt and a bias across the nanoribbon of 0.2 Volt. 

 Graphene nanowire device structure, with gates

Larger systems

The semi-empirical description corresponds effectively to a single-zeta basis set, but offers similar accuracy (or better!) as a double-zeta polarized ATK-DFT basis set. Therefore, you can do larger calculations without compromising the accuracy.

Right: An (8,4) carbon nanotube resting on two metallic electrodes. The transport system contains 1,440 atoms in total. By modulating the electron density in the central region via the 3 metallic gates, which are screened by the dielectic region, band-to-band tunneling can be observed, as shown in the lower picture which depicts the valence and conduction band edges along the tube [1]. Different colors correspond to different gate voltages on gate B in the top right picture. All calculations were performed using a preliminary edition of ATK-SE 2009.06.

 84 CNT with gates 

84_cnt_with_gates_b2b_tunneling.png

[1] H. H. B. Sørensen, P. C. Hansen, D. E. Petersen, S. Skelboe, and K. Stokbro, Efficient wave-function matching approach for quantum transport calculations, Physical Review B 79, 205322 (2009); also available as arXiv:0804.4306v3

Correct prediction of band gaps

Specifically, ATK-SE uses the extended Hückel method, and since the Hückel parameters have been fitted to the correct band structure, the semi-empirical approach avoids the band gap problem of DFT and gives a correct band structure of semiconductors.

Right: Band structure of Si, computed with ATK-SE 2009.06.

 Si bandstructure

New edition of VNL and NanoLanguage

The 2009.06 package introduces the next generation of QuantumWise's graphical user interface, Virtual NanoLab (VNL) and the scripting interface to ATK, NanoLanguage.

VNL is designed to support the ATK work-flow as conveniently as possible for the user. This latest edition introduces several improvements compared to earlier version, but the main objective remains the same, to help the user in setting up, running, and analyzing the calculations.

For more details about the new features, see below!

 

Support for GPAW

GPAW   ASE

See below for details!

 VNL_2009.06_Screenshot

 

 

Virtual NanoLab and NanoLanguage 2009.06

VNL is designed to support the ATK work-flow as conveniently as possible for the user. This latest edition introduces several improvements compared to earlier version, but the main objective remains the same, to help the user in setting up, running, and analyzing the calculations.

VNL 2009.06 contains

  • Databases
    • molecules (same as in older VNL editions)
    • crystals (greatly extended compared to older versions)
    • fullerenes
  • Support for generating NanoLanguage scripts for electronic structure and transport calculations with ATK-SE (support for ATK-DFT will be added later)
  • Support for electronic structure calculations with GPAW (see below)
  • A new tool, the Custom Builder, a novel plug-in concept! (More details to follow!)
  • Built-in file browser
  • Vastly improved 3D performance
  • Proper band structure calculations and plots by symmetry points, and several other minor feature improvements

As can be seen, some components known from the older versions of VNL are yet missing, these will be included in subsequent releases.

The scripting interface to ATK, NanoLanguage, also continues to evolve. In this release, the "grammar" of the language, the logic of how to set up calculations and geometries, has been updated and improved, and this means that things work a little bit differently compared to earlier versions. The changes are however quite small and easy to learn.

 

Unified, open file format

All calculations, structures, etc are stored in NetCDF files, in an open format. The same file is used for storing the results of a calculation as for the self-consistent density which can be used to restart the calculation or perform post-scf analysis. The contents of the NetCDF files can easily be inspected in VNL, or third-party tools.

 

Extending the platform: support for external codes (GPAW)

The 2009.06 version also includes support for running GPAW from VNL (and NanoLanguage). GPAW is a grid-based DFT code developed at the Danish Technical University, and is specifically designed for applications within catalysis and surface science. More information can be found at the GPAW home page and in the manual.

The native interface to GPAW is the Atomistic Simulation Enviroment (ASE), which comes pre-installed in NanoLanguage 2009.06.

QuantumWise plans to add support for other external calculators in future editions of VNL. This will expand the range of usability and create a platform solution, where different codes can share definitions of e.g. structures, while providing a uniform interface to setting up calculations and visualizing the results.

 

Licensing

The new package uses a new licensing platform compared to the older releases; QuantumWise now uses Sentinel RMS from Safenet. It is our hope that this will mean less administrative burdens for the end-users in managing the licenses. A license is required to run the software; please fill out the trial request form for details!

 

Comparing ATK-SE and ATK-DFT

ATK-SE should be seen as a complement to ATK-DFT, and not a replacement of it.

After all, DFT is more accurate at describing structures involving unusual combinations of elements, or atoms in new configurations. On the other hand, the semi-empirical approach (specifically, ATK-SE uses the extended Hückel method) avoids the band gap problem of DFT since the parametrization is fitted to the correct band structure.

A method which involves parameters, as the extended Hückel model does, is only as good as its parameters. QuantumWise has therefore taken great care to provide parameters that give an accurate description of typical systems that users would like to study. Most notably, this includes various semiconductor structures like silicon, graphene, nanotubes, etc. The results obtained with these parameters are just as accurate as for DFT, but as noted above the calculations are much faster!

Therefore, which code that provides the best solution for a particular problem may require some careful considerations. QuantumWise will of course offer customers advise and consultation to aid in making the choice.

For the moment, this initial releaes of ATK-SE also has some limitations compared to ATK-DFT, that should be considered:

  • ATK-SE 2009.06 is only released for Linux platforms (32 and 64 bit)
  • The code is not yet parallelized
  • Some analysis functions known from ATK-DFT are not yet implemented
  • Spin is not yet implemented

 

Feedback, comments, etc

QuantumWise highly values feedback from users. It's the only way we can continue to evolve the products in a direction that provides increased value to our customers. If you have any comments, questions, suggestions, or any other kind of feedback about our products, please contact us!

We hope you will all enjoy working wit ATK-SE as much as we enjoyed making it (and using it - we also use our own products extensively)!

 

The QuantumWise Team
Copenhagen 2009-07-01

 

 
 
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