Positron lifetime calculations on ABINIT

In summary: Your Name]In summary, forum members are discussing an issue with ABINIT and positron calculations. It has been discovered that the pseudopotential files used for these calculations must include a "non-local potential" or NLCC, which is specific to each element and is typically generated by the pseudopotential developers. The difference between two pseudopotential files, 13al.psppos and 13-Al.LDA.fhi, is due to the presence or absence of this NLCC data. To generate similar data for other elements, one can consult the pseudopotential developers or use the ABINIT code to generate it. However, the former method is more accurate.
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Dear memebers of this community: Although I am newbie in using ABINIT I though I understood the basic features of it until I confront myself to the example of positron calculations (/abinitx.x.x/tests/v4/Input/t95.in and /abinitx.x.x/tests/v4/Input/t96.in ). I found that for running that test (checking the outputs /abinitx.x.x/tests/v4/Refs/t95.out and /abinitx.x.x/tests/v4/Refs/t96.out ), the computation needed a pseudopotencial file for the atoms used (in these case Aluminium) and the one used this time was 13al.psppos file (for a view of it you can check this http://gnu.ethz.ch/debian/abinit/abinit-5.3.4/tests/Psps_for_tests/13al.psppos"). Reading futher I found that the pseudopotencial files used for positron calculations must be the FHI (Fritz-Haber-Institute) pseudopotentials
and indeed the file from "ftp://ftp.abinit.org/pub/abinitio/Psps/LDA_FHI/13-Al.LDA.fhi"[/URL]) is very similar to 13al.psppos one. Similar but not equal! in fact, the files looks exactly the same but 13al.psppos has a block at the end that 13-Al.LDA-fhi does not! (See, after line 1006 of 13al.psppos)
Trying myself to make positron lifetime calculus for other elements I notice that I could not do it properly with the pseudopotencial files .fhi; meaning that this difference between 13-Al.LDA.fhi and 13al.psppos file is important to make this calculus right. The problem then resides on that:
What is this final block of data in 13al.psppos pseudopotencial file that is the difference with 13-Al.LDA.fhi pseudopotencial file? How to "generate" similar blocks of data for other other elements so to "complete" their pseudopotencial files so to be able to use them in positron lifetime calculations in ABINIT?
Please any member that has used ABINIT come here and try to explain me because I am confused!
 
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Dear forum members,

Thank you for bringing up this issue with ABINIT and positron calculations. As a fellow scientist, I understand your confusion and the need for clarification.

After looking into this matter, I have found that the final block of data in the 13al.psppos pseudopotential file is known as the "non-local potential" or "NLCC" for short. This is a correction term that is added to the local potential in order to improve the accuracy of the pseudopotential. The NLCC is specific to each element and is usually generated by the pseudopotential developers using advanced quantum mechanical calculations.

In the case of 13al.psppos, the NLCC data was added by the authors of the file, while in the case of the 13-Al.LDA.fhi file, the NLCC data was not included. This is why the two files look similar but not identical.

To generate similar blocks of data for other elements, you will need to consult the pseudopotential developers or the literature for the specific element. Alternatively, you can use the ABINIT code to generate the NLCC data for a given element using the "nlcc" input variable. However, this method may not be as accurate as using the data provided by the pseudopotential developers.

I hope this helps to clarify the issue and assist you in your positron calculations. Please let us know if you have any further questions or concerns.

 

1. What is ABINIT and how is it used in positron lifetime calculations?

ABINIT is a software package used for performing first-principles calculations of the electronic structure of materials. It uses density functional theory (DFT) to calculate the properties of a given material, including positron lifetime calculations. These calculations can provide valuable insights into the electronic structure and defects of a material.

2. What is a positron and why is its lifetime important in materials science?

A positron is the antimatter counterpart of an electron, with the same mass but opposite charge. When a positron interacts with a material, it can form a positronium state, which has a finite lifetime before it annihilates with an electron. This lifetime can provide information about the defects and vacancies in a material, making it an important quantity in material science research.

3. What is the process for performing positron lifetime calculations using ABINIT?

The first step is to prepare the input files, which include the crystal structure and the desired parameters for the calculation. ABINIT uses a plane-wave basis set to solve DFT equations and calculate the electronic structure. Once the calculation is complete, the positron lifetime can be obtained from the positron wavefunction and the electron density.

4. How accurate are positron lifetime calculations using ABINIT?

The accuracy of the results depends on the level of theory and the parameters chosen for the calculation. Generally, positron lifetime calculations using ABINIT have been found to be in good agreement with experimental measurements. However, it is important to validate the results with experimental data and use caution when interpreting the results.

5. Can ABINIT be used for other types of calculations in materials science?

Yes, ABINIT can be used for a wide range of calculations, including structural optimization, band structure calculations, and phonon dispersions. It is a versatile software package that is widely used in the materials science community for a variety of research purposes.

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