The ABINIT Users Mailing List ( CLOSED )

[Xavier Gonze <gonze@pcpm.ucl.ac.be>]

Dear Tao Junguang,

Please, send your input files, as well as appropriate
parts of the output files ...

Xavier

On 30 Apr 2007, at 11:15, #TAO JUNGUANG# wrote:

> Thanks very much first. Then followed another question.
>
> Actually, after found the best coordination, I let the software  
> optimize the structure by setting "optcell 1 ionmov 2". From the  
> output file, at the very end, we will get the best fitted lattice  
> constants and corresponding total energy. Using the best fitted  
> lattice constants, I made a second keeping all the other parameters  
> unchanged. I get another total energy which is not the same as the  
> first one. They are supposed to be the same, am I right? Why this  
> happens? I mean, how come they are different?
>
>
>
>
> -----Original Message-----
> From: Anglade Pierre-Matthieu [mailto:anglade@gmail.com]
> Sent: 2007年4月30日 2:56 PM
> To: forum@abinit.org
> Subject: Re: [abinit-forum] how to optimize the structure parameters.
>
> Hi,
>
> First I would say that your order to perform cell optimization looks
> correct as long as you do not await phase change under stress. Yet it
> would probably be more efficient to perform directly a global
> optimization of both atomic and cristal coordinate.
> Second, I can not comment on correctness of experimental ratio. But
> using your procedure you will likely fall close to at least a DFT
> local minima. So, as long as DFT is correct, your approach is OK.
>
> regards
>
> PMA
>
> On 4/30/07, taoj0003@ntu.edu.sg <taoj0003@ntu.edu.sg> wrote:
> > when using abinit(maybe also some other software) to optimize the  
> > structure, a problem really puzzled me-what is the best procedure?
> >
> > let me make this more clearly. To optimize the structure, here is  
> > one procedure:
> >
> > First, if there are more than one atom in the cell, we need  
> > feagure out all of the optimized coordinations. Abinit make this  
> > part easy to do thanks to the "ionmov".
> >
> > Then we need to optimize lattice constants.But how? Just keep  
> > their experimental ratio and optimize the volume or adjust every  
> > values (a, b ,and c) near the experiment values until it reached  
> > the lowest total energy? If you do it the first way, I may ask, is  
> > the experiemnt ratio correct for using in the simulation? 
> > ( because, simulation always deviates from experiment somehow).
> >
> > The second part really make me crazy. There are also some cross  
> > section effect. And even should the seccond part go first?
>
>
> --
> Pierre-Matthieu Anglade