Only gamma point is needed for isolated molecules or atoms. Spin polarization can be included; you need a initial antiferromagnetic configuration for H2. But without spin, the results should be close because H2 molecules don't have net spin polarization.
H2 should behave well with most functionals. Here are some of my results of the binding energy (eV per bond): PBE (siesta): 4.76 PBE (vasp): 4.54 HSE06 (vasp): 4.53 Hope this helps. Haibo 2011/2/28 Süle Péter <[email protected]>: > > 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 >> >> >> >> >
