[Pw_forum] ab initio vs. first principles.

[Eyvaz Isaev]

Dear Hongsheng,

You can find the answer in 
 
http://en.wikipedia.org/wiki/Ab_initio

Below is what is described on the webpage:

>From Wikipedia, the free encyclopedia 

The Latin term ab initio means from the beginning and is used in several contexts:
 
in science: A calculation is said to be "ab initio" (or "from first principles") if it relies on basic and established laws of nature without additional assumptions or special models.
For example, an ab initio calculation of the properties of liquid water might start with the properties of the constituent hydrogen and oxygen atoms and the laws of electrodynamics. From these basics, the properties of isolated individual water molecules would be derived, followed by computations of the interactions of larger and larger groups of water molecules, until the bulk properties of water had been determined.

In our computational materials Science we use only atomic numbers (and experimental atomic positions which are not necessarily required) and 
quantum-mechanics laws that make our calculations "ab initio" or "from first principles".

And no one can explain "ab  initio" results "from first principles". as they are the same, no difference between them except that "ab initio" refers to Latin, and "from first principles" is in English.

Bests,
Eyvaz.

-------------------------------------------------------------------
Prof. Eyvaz Isaev, 
Theoretical Physics Department, Moscow State Institute of Steel & Alloys, Russia, 
Department of Physics, Chemistry, and Biology (IFM), Linkoping University, Sweden 
Condensed Matter Theory Group, Uppsala University, Sweden 
Eyvaz.Isaev at fysik.uu.se, isaev at ifm.liu.se, eyvaz_isaev at yahoo.com


--- On Sun, 12/21/08, Hongsheng Zhao <zhaohscas at yahoo.com.cn> wrote:

> From: Hongsheng Zhao <zhaohscas at yahoo.com.cn>
> Subject: [Pw_forum] ab initio vs. first principles.
> To: "PWSCF Forum" <pw_forum at pwscf.org>
> Date: Sunday, December 21, 2008, 2:49 PM
> Hi all,
> 
> Some times we say ab initio, sometimes first principles. 
> Actually,
> I find in many case people use them to explain one another.
>  But the fact may be not the case, who can give some hints
> on the differences between ab initio and first principles? 
> 
> Regards,
> -- 
> Hongsheng Zhao <zhaohscas at yahoo.com.cn> 
> Xinjiang Technical Institute of Physics and Chemistry
> Chinese Academy of Sciences 
> GnuPG DSA: 0xD108493
> 2008-12-21
> 
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