Dear Aleksander, Thank you very much for all of you suggestions.
How did you optimize the basis? Did you use the program in Util folder in siesta?* This is more a conceptual problem. How the system is prepared experimentally? Is it an MBE deposition of atoms, or surface prepared by annealing in vacuum, where the Mn atoms come from?* Ga1-xMnxAs thick films (1.7<=x>=9 %) were grown on GaAs(001) substrates by low-temperature (180-300 oC)molecular beam epitaxy using As2. The surface orientation is (001). *What is the unit cell size that you use? Is it (2x4)?* I have no idea what kind of cell size to choose when I have Ga-terminated surface, where two Ga atoms are substituted by Mn atoms. Do you know any paper, book, tutorial where I can find something about reconstructions? How can I construct such a surface. How to connect such a reconstructed unit cell with a bulk which have different stechiometry and unit cell? Magdalena 2010/7/28 Alexander Vozny <[email protected]> > For 500 Ry I get zero forces on atoms for bulk >> GaAs, whereas for 300 Ry I still have some not vanishing values. >> > That's a bit surprising for me. Usually forces should vanish around > 200-250Ry. So I'd rather recheck whether you have a good k-grid. > Soft confinement of orbitals could also help a lot, especially since you > need very good convergence in forces. > Here is my optimized GaAs basis: > > %block PAO.Basis > As 3 -0.195 > n=4 0 2 E 73.28644 5.7 > 6.879 4.278 > n=4 1 2 E 44.09132 6.25442 > 8.04645 5.19876 > n=4 2 1 E 97.53993 1.03121 > 7.50695 > > Ga 3 > n=4 0 2 E 80.12335 5.74628 > 7.16526 4.82650 > n=4 1 2 E 87.59084 7.11605 > 7.61660 4.41252 > n=4 2 1 E 93.09519 0.13086 > 6.26045 > %endblock PAO.Basis > > Or you could try to let SIESTA automatically soften the orbitals as > implemented in SIESTA 3 (PAO.SoftDefault). > > > > I want to study a different configuration of one pair of Mn ions on the >> surface of GaAs. I want to see the difference in the energy , electronic >> structure, >> > > This is more a conceptual problem. How the system is prepared > experimentally? Is it an MBE deposition of atoms, or surface prepared by > annealing in vacuum, where the Mn atoms come from? > Depending on the preparation procedure the final geometry can be very > different. > You need to know that you are modeling the right thing, otherwise you'll > spend ages of time on getting very accurate results on the system which is > wrong from the very beginning. > What is the surface orientation? Is it (100)? > What is the unit cell size that you use? Is it (2x4)? > What is the initial surface reconstruction? GaAs does not exist > unreconstructed. It would take a lot of time for CG procedure just to relax > the surface if you don't provide the right geometry. >
