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

[Sashank Kasiraju]

Hi,

Thank you Marcin, I will look into that. Yes, I did try setting the initial
magnetic moment to 0 for both atoms in a different calculation with the
exact same result of Hydrogen molecule splitting into 2 atoms. And the
total magnetic moment at the end of relaxation was back to 2.

The results converged only in the case of ispin=1.


On Mon, Apr 15, 2013 at 11:51 AM, Heine Hansen <heineahansen at gmail.com>wrote:

> Hi,
>
>
> I think I have seen H2 dissociate as well, but I forgot the details.
>
> I note you do not use set_initial_magnetic_moments. Have you tried to set
> the initial_magnetic_moments to e.g. (0., 0.), (1., 1.) and (1., -1.)?
>
> What is the MAGMOM-tag in the INCAR? The vasp default is MAGMOM = 1 1
> (which you probably do not want).
>
>
> Best Regards,
> Heine
>
>
>> 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
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>
>


-- 
Regards,
Sashank Kasiraju,
PhD Student,
Dept. of Chemical Engineering,
University of Houston.
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