Institute of Theoretical Physics
Department of Applied Theoretical Physics
Frequently asked Questions
What is the PAW Method?
The Projector Augmented Wave method is a simulation algorithm to obtain the total energy, electron distribution and atomic structure and dynamics. The term PAW is often also used as short hand for the CP-PAW code developed originally by Peter Blöchl.Find here further informtion
Where can I find a description of the PAW method?
The original reference is Peter E. Blöchl, Phys. Rev. B 50, 17953 (1994). Some of the ideas have been shaped during earlier pseudopotential work described in Peter E. Blöchl, Phys. Rev. B 41, 5414 (1989). There is also a publication focusing on people new to PAW: "The Projector augmented wave method: ab-initio molecular dynamics with full wave functions"Peter E. Blöchl, Clemens J. Först and Johannes Schimpl, submitted to Bull. Mater. Sci. (Dec. 31, 2001)
Here is a introductory presentation on ab-initio methods and here a presentation specificly on the PAW Method given by P. Bloechl at the CAMD Summer School 2010.
Are there other implementations of PAW besides the CP-PAW code?
I am aware of a view other implementations of the PAW method-
N.
A. W. Holzwarth, G. E. Matthews, R. B. Dunning, A. R. Tackett, and
Y. Zen g, Phys. Rev. B 55, 2005 (1997).
The resulting PWPAW code is freely available: Computer Physics Communications 135 329-347, 348-376 (2001) - The ABINIT code
- There is a PAW code in the group of M. Valiev and J.H. Weare at the University of California, San Diego.
- The PAW method has also been implemented by W. Kromen into the ESTCoMPP code of Blügel and Schröder.
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PAW has been implemented as option in the VASP code
G. Kresse and D. Joubert, Phys. Rev. B. 59, 1758 (1999) - ABINIT
- Another branch of methods uses the reconstruction of the PAW method, without taking into account the full wave functions in the self-consistency. Following chemist notation this approach could be termed "post-pseudopotential PAW". This development began with the evaluation for hyperfine parameters from a pseudopotential calculation using the PAW reconstruction operator (Van de Walle, C.G. and Blöchl, P.E., 1993, Phys. Rev. B 47, 4244) and is now used in the pseudopotenital approach to calculate properties that require the correct wave functions.
What is the relation between PAW and the pseudopotential approach?
The PAW method is an all-electron method, that is the full wave functions including their nodal structure are properly defined, whereas the pseudopotential method deals with nodeless wave functions. The PAW method is more rigorous, and can be made exact by converging series expansions. (The current implementation in CP-PAW still uses the frozen core approximation.) The pseudopotential approach can be derived from the PAW method by a well-defined approximation. This approximation discriminates the pseudopotential approach from all-electron methods. They can cause transferability problems of the pseudopotentials if the density deviates strongly from that of the reference atom. In practice the errors are larger for high-spin configurations.By providing the full wave functions and densities, the PAW method provides quantities such as electric field gradients
or hyperfine parameters directly. In contrast the full density needs to be reconstructed in the pseudopotential approach.
The PAW method uses extensively the numerical methodology developed for the pseudopotential approach and for the LMTO method. This results in fast algorithms, and a close similarity between those methods.
How do I obtain access to the CP-PAW code?
Please note that the CP-PAW code is not easy to use, and requires some experience. Therefore, it is advisable if you have been trained in ab-initio molecular dynamics or if you have a colleague who is willing to help you during your first steps. It is certainly not the kind of code you want to use "on a side".
You require a license from Clausthal University of Technology to be able to access the code. There is a small fee for non-profit research organizations and an appropriate fee for commercial entities.
To request a license, please go to the PAW download page, where you will be asked to fill an electronic form with your contact details and you will find further details on the process.
If you encounter problems, please contact
Prof. Dr. Peter E. Blöchl
Address:
Dept. of Applied Theoretical Physics
Institute of Theoretical Physics
Clausthal University of Technology
Leibnizstr. 10
D-38678 Clausthal-Zellerfeld
Germany
phone: +49(5323)722555
fax: +49(5323)723116
E-Mail: Peter.Bloechl@tu-clausthal.de