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["#TAO JUNGUANG#" <TAOJ0003@ntu.edu.sg>]

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