[Pw_forum] How to using gamma point calculation with high efficiency

[Stefano Baroni]

On Jun 29, 2008, at 4:44 AM, vega lew wrote:

> > whether or not a gamma p oint calculation is sufficient is not
> > determined by what other people do, but by the physics of the
> > problem.
>
> I have realized that. Late time maybe I doesn't say it in a right  
> way. I'm using gamma point calculation
> is not all because other people do so, but also many scientific  
> papers of high impact and high quality,
> such as paper of American Physical Society

> and American Chemical Society

even worse. i would trust more a colleague next dore (whom, at least I  
could tease and ask questions) than a journal, ANY journal, no matter  
its impact factor, publishing company, title ...

> said using 2X2X1 mesh of k points
> result in no large difference in energy of geometry from the gamma  
> point only calculation.

I am afraid you do not exactly what you are talking about. who says  
what? what is good fo a system may be totally wrong for another,  
unless you know exactly WHY it is good in one case and you are sure  
that the same argument holds for the second. this only YOU can say,  
after sweating quite a lot to understand by yourself, which, I  
understand, you are not quite prepared to do

> It's accepted
> by most of scientists do the similar job for many years. I think  
> it's not necessary to validate it by my self
> because of the weakness of our calculation condition.

if you are not "strong" enough (as opposed to "weak", to use your  
words) to accomplish a task fairly, you simply have to choose a  
different task that suits your strength more ...

> >that reminds me, you still owe us an explanation about
> > the difference between 'commercial' and 'academic' calculations.
> > i am _very_ curious about this.
>
> I don't have enough authority to illustrate the difference beteen th  
> e two. I only saying something from my
> own brain. I think Q-E is more suitable for scientific research,  
> because of its free and open-source. And
> another very important thing is Q-E also accepted by many resarchers  
> who used Q-E and doing excellent
> calculation. Also many pieces of work published on high quality and  
> high impact Journals, like Nature Materials,
> Journal of the American Chemical Society et al...

it sounds like somebody led you to believe that the purpose of science  
is to publish in high-impact journals. are you sure this is really the  
case?

> But for comercial software, it cost a lot of money and the
> source code is not open for their copyright. So it's much more like  
> a black box. We can't know any detail that
> how the results comes out. Maybe it's more accurate,

demonstrabily, it is not

> but we can't believe it until we see the source code.

finally, we agree on at least one point

If I were to describe in one sentence what makes the difference  
between modern science and ancient knowledge systems, it is the role  
played in the former by the "doubt": never trust a truth unless you  
can give by yourself a correct answer to a legitimate question. and  
reproducibly so. I am sure you are studying to become a modern  
scientist, don't you?

regards - SB

---
Stefano Baroni - SISSA  &  DEMOCRITOS National Simulation Center -  
Trieste
http://www.sissa.it/~baroni / [+39] 040 3787 406 (tel) -528 (fax) /  
stefanobaroni (skype)

La morale est une logique de l'action comme la logique est une morale  
de la pensée - Jean Piaget

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