[ase-users] Spin polarized calculation of H2 Molecule gives different potential energy

[Marcin Dulak]

Hi,

you should check the occupation numbers:
http://cms.mpi.univie.ac.at/vasp-forum/forum_viewtopic.php?4.490

Best regards,

Marcin

On 04/12/2013 09:41 PM, Sashank Kasiraju wrote:
> Dear ASE/VASP users,
>
> This is my first query, so if I miss something or if I am unclear 
> please bear with me. I am a relatively new vasp user.
>
> I was trying to do this simple calculation for finding the potential 
> energy of H2 Molecule. I got 2 different results with and without 
> spin-polarized calculation. I am using "/vasp.5.3.3 18Dez12 (build Jan 
> 17 2013 09:57:53)/"
>
>  1. When ispin=1 (non-spin polarized) , the bond length of the relaxed
>     configuration was around the 0.747 A which is close to the
>     experimental value with a potential energy of about (-7.04 ev)
>  2. When ispin=2 (spin-polarized), the bond length of relaxed
>     structure was 3.801 A, i.e. the hydrogen atoms in the molecule
>     moved apart and exist as 2 separate H atoms with the potential
>     energy of about (-2.47 ev)
>
> You can find the python script below. Both the cases have the same 
> python script (except for the presence/absence of ispin tag i.e. case 
> 1: no ispin tag, case 2: ispin=2). I used the ibrion=2 tag for ionic 
> relaxation. I will be happy to provide any other information/outputs 
> if required. Can you please let me know why this is happening? Or if I 
> am going about it totally wrong?
>
> Thanks in advance!
>
> *Script: *
>
> from ase.visualize import view
> from ase.calculators.vasp import Vasp
> from ase.io <http://ase.io> import write
> from ase.structure import molecule
> from ase.io <http://ase.io> import read
> import os.path, os
>
> os.environ['VASP_EXEC']='vasp_std'  # define the vasp executable here
>
> file=open('Hydrogen_Energy.txt','a')
> name = 'H2_Energy'+ '.traj'
> atoms= molecule('H2')
> atoms.center(vacuum=10)
> calc=Vasp(xc='PBE',
>           gga='RP',
>           ibrion=2,
>  lscalapack=False,
>           nsw=500,
>           nelm=200,
>           ediffg=-0.01,
>           prec='Accurate',
>           encut=540,
>           ediff=1E-6,
>           kpts=(1,1,1),
>           ismear=0,
>  ispin=2,
>  sigma=0.01,
>  lwave=False,
>           lcharg=False,
>           ialgo=48,
>           lreal='False',
>           idipol=4,
>           ldipol=True,
>           dipol=(0.5,0.5,0.5),
>  gamma=True,
>           npar=2)
> atoms.set_calculator(calc)
> e = atoms.get_potential_energy()
> write(name, atoms)
> file.write(str(e)+'\n'+'In (ev)')
> file.close()
>
> Warm Regards,
> Sashank.
>
> -- 
> Regards,
> Sashank Kasiraju,
> PhD Student,
> Dept. of Chemical Engineering,
> University of Houston.
>
>
> _______________________________________________
> ase-users mailing list
> ase-users at listserv.fysik.dtu.dk
> https://listserv.fysik.dtu.dk/mailman/listinfo/ase-users

-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://listserv.fysik.dtu.dk/pipermail/ase-users/attachments/20130414/8a074b69/attachment.html>