Hi Natalia, Thank you very much! It was my fault. The calculation results are satisfactory. The E(binding) is 4.778086 eV (per bond) and the bond length is 0.7457734 Ang. Thank you again! Best wishes! 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 18:53 收件人: [email protected] 主题: Re: 答复: [SIESTA-L] H2 binding Energy 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 >>>> >>>> >>>> >>>> >>> >> > >
