The ABINIT Users Mailing List ( CLOSED )

[Marc Torrent <marc.torrent@cea.fr>]

Dear Pio,

1) Concerning the convergence behaviour with respect to ecut:
It seems that the results you get are the same as those published (for 
pwpaw code) at 
http://www.wfu.edu/%7Enatalie/papers/pwpaw/periodictable/atoms/Al/Al_dat,
provided that you use the following translation formula:
ecut_abinit=gcut_pwpaw**2/2
So, this atomic data file, created by PWPAW group seems to have a slow 
convergence vs ecut; it could be improved...

2) Concerning the energy difference:
a) did you try with a norm-conserving pseudopotential ? is the behaviour 
the same in that case...
b) did you have a look at the decomposition of energy (at the end of 
each datasry in output file) ? you could perhaps identify which term of 
energy is responsible for the non-zero value...


Marc Torrent
CEA-Bruyeres-la-Chatel
France

Pio Baettig a écrit :
> Dear Abinit-users,
>
> I have a small problem using PAW implemented in Abinit.
> I downloaded the Al-PAWs (LDA and GGA) from
> http://www.wfu.edu/%7Enatalie/papers/pwpaw/periodictable/periodictable.html
> and started doing convergence tests with respect to number of K-points and
> the cutoff-energy. I am using Abinit 5.3.4
>
> The first thing I noticed, is that the convergence with respect to the
> energy-cutoff is quite slow, for Al around 35 Ha are needed to converge the
> energy to one mHa. (8*8*8 k-points seem also to be sufficient.)
>
> I tried the same calculations for a cubic unit cell
> (a=4.05Angst, pos. 0.0 0.0 0.0;0.0 0.5 0.5;0.5 0.0 0.5;0.5 0.5;0.0 , 
> nband=40)
> and for a rhombohedral unit cell
> (a=4.05/SQRT(2), alpha=60 deg, pos:0.0 0.0 0.0, nband=10)
> and then took the difference of
> E(cubic)-(4*E(rhomb)) which should converge to zero quite fast. (even 
> though
> the number of k-points in the irreducible Brillouin-zone is not the same
> for the same mesh in the full BZ, the convergence should still be good),
> but the energy-difference converges to about 0.28 Ha, which I interpret,
> that I cannot compare energies of different structures.
>
> I did not yet repeat the same calculations with another element in order to
> check whether the problem is with the Al-PAWs or with the method. I hope 
> not
> to have forgotten something important in the inputs.
>
> Please find attached the inputs used for the cubic and the rhombohedral 
> case.
> I also attach a table with the energies. Lines are for the different 
> k-point-
> meshes, columns for the different cutoff energies.
> First comes LDA, then GGA,
> for each I put a table with the energies of the cubic unit cell, then the
> rhombohedral unit cell, then the difference (c-4r)
>
> If someone has some insight into the behaviour, I would be very grateful
>
> Best regards,
>
> Pio Baettig