Hello Leila, Did you do a spin-polarized calculation of the atom as well? (see attached fdf)
Regards, Natalia On 3/1/11, leila <[email protected]> wrote: > Dear Natalia, > Thank you for your reply. I learnt a lot according to your email. > However, the FixSpin tag didn't really guide me to the proper results. I got > the binding energy of -7.17 eV, rather than -4.8 eV in your last mail. > Thank you very much! > Yours sincerely, > Leila > > -----邮件原件----- > 发件人: Natalia Martsinovich [mailto:[email protected]] > 发送时间: 2011年3月1日 2:10 > 收件人: [email protected] > 主题: Re: [SIESTA-L] H2 binding Energy > > Hello Leila, > > I see that a spin-polarized calculation with your input file gives a system > with two spin-up electrons. In this case, yes, the H atoms want to move > apart to become two independent atoms. So, in the spin-polarized > calculation, you need to fix the initial spin to zero. > FixSpin T > TotalSpin 0.0 > Then I get the H2 binding energy of -4.8 eV. (It will be a little smaller > when corrected by BSSE). > > Spin polarization is essential for the correct description of the H atom > (not essential for the molecule). > > Also, as Haibo said, only the gamma point is needed for an isolated > molecules, more k-points just take more time. > > Regards, > > Natalia > > On 2/28/11, Haibo Guo <[email protected]> wrote: >> 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 >>>> >>>> >>>> >>>> >>> >> > >
H-SpinPol.fdf
Description: application/vnd.fdf
H2-SpinPol-Fix.fdf
Description: application/vnd.fdf
