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["zeng zhenhua" <myid520@hotmail.com>]

Hello Homolya and abinit users:
   I think I was wrong when I said “Note, I find the “optcell” can’t 
be used to automaticly optimize the acell of hydrogen”. The reason why I 
said that is “optcell” doesn’t work when the used acell bigger than 0.9 
experiment data of solid hydrogen (inter-atom force is vary small at these 
location). Now the first step when I calculate the accurate acell is 
calculating the total energy at a acell range with different acell step. 
Then reducing the acell range with varying step form 1bohr to 0.1bohr .The 
rough acell is the acell at lowest total energy . Using the rough acell, 
the accurate acell can be obtained easily. Using this method the accurate 
acell calculated at extremely low temperature of hydrogen is only about 
half of experiment data.(The experiment data is 2*3.75 6.12 Angstrom at 
4k,calculated result is 2*1.98 3.23 Angstrom) Now I’m calculating acell of 
several element for practicing. So I also calculate the acell of solid hcp 
He, bcc Li, hcp Be, bcc Na and hcp Mg. I find the calculated acell value of 
He is only 80% of experiment data, the Li is 90%,the Be is about 85%.But 
the calculated value of Na and mg have been within 2% experiment data. So I
’m puzzled about the accuracy of abinit on light element . In addition all 
pseudopotentials almost give same result.

Zhenhua Zeng
Department of Applied Physics  Hunan University  PR China 410082
Tel: +86 731 8821643



> From: Steven Homolya <Steven.Homolya@spme.monash.edu.au>
> Reply-To: forum@abinit.org
> To: forum@abinit.org
> Subject: Re: [abinit-forum] accurate acell and structure of hydrogen
> Date: Tue, 25 Nov 2003 12:32:59 +1100
>
> On Tue, 25 Nov 2003 01:29 am, zeng zhenhua wrote:
> > Dear ABINIT users:
> > I have been read the tutorial of abinit several times, but I have some
> > questions about tutorial 1 and 2. firstly, In tutorial 2,acell is given
> > through the convergence on the interatomic distance and atomisation 
energy.
> > But I think this acell is very rough.. I want to known how to get 
accurate
> > acell of hydrogen. Note, I find the “optcell” can’t be used to
> > automaticly optimize the acell of hydrogen . Secondly, although we 
known
> > the structure of hydrogen is hcp, it is treated as sc in tutorial 1 and 
2 .
> > I want to known how to judge which structure it is, it is hcp, sc or 
some
> > structure else. Do you have any suggestion for these problems? Thanks 
in
> > advance.
> > Zhenhua Zeng
> >
>
> As stated in their titles, the tutorials are about the hydrogen (H_2)
> _molecule_, not about the solid form you mention, which occurs only at
> extremely high pressures! It should be evident what acell means in this
> context, why it needs to be fairly large, and why it's not "optimised".
>
> --
> Steven Homolya
> School of Physics and Materials Engineering
> Monash University VIC 3800
> Australia
> Tel: INT +61 3 9905 3694
> Fax: INT +61 3 9905 3637

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