Dear Leila,
for me using siesta-2.0.2 with your fdf file (GGA/PBE, 5X5) 0.75 -31.5205 eV/H2 10. -25.4867 inf -24.3496 Ec= ~ -3.5854 eV/atom (e.g. -7.17 eV bond energy) which is not bad. I mean one can not necessariliy expect with GGA a better value. Hybdrid functionals should give better results. The issue of better VASP values should be discussed in a more detail by experts since indeed quite oftenly happens. Best regards, Péter Sule ---------------------------------------------------- Dr. Peter Sule senior research associate Institue for Technical Physics and Materials Science (MTA-MFA), Konkoly-Thege M. 29-33, Budapest, Hungary tel.: (36) 1 392 2222/3605 fax.: (36) 1 392 22 73 www.mfa.kfki.hu/~sule / [email protected] ----------------------------------------------------- On Mon, 28 Feb 2011, leila wrote:
Hi, everyone, I want to do some calculations on the H effect in Fe, before which I have to promise the accuracy of H potential. I first make a simple tests of the H2 properties, including the H-H distance in H2, and also the binding energy (Defined as the energy difference of the H2 molecular and two isolated H atom). I find the H-H distance is around 0.75 Ang, which is near to the experimental value of 0.741 Ang, for both LDA and GGA pseudopotential. However, the binding energy is always not correct, calculated to be around -7.2 eV (The experimental and VASP results are all around -4.55 eV). My input file for H are in the attachments. I don’t know where the issues are. Could anybody help me? In addition, I find that the spin polarization contributes a lot in the H2 calculations. When I add the spin polarization effect in the VASP and SIESTA calculations, the H-H distance becomes to 2.89 Ang, and the binding energy is approaching to 0 eV. Can anyone explain this to me. Because Fe is magnetic materials, I have to consider spin polarization effect in my calculation. Thank you in advance! Yours sincerely, Leila
