[Pw_forum] ab initio vs. first principles.

Stefano Baroni baroni at sissa.it
Mon Dec 22 09:49:39 CET 2008

(although quantum chemists may disagree to some extent)

On Dec 22, 2008, at 2:47 AM, Leonardo Matheus wrote:

> A small doubt that I had while following this discussion, please  
> someone correct-me if I'm wrong:
> Is the following definition right?
> "[in ab-initio calculations we] do not make any assumption, such as  
> concerning models and/or fitting parameters."
> I'm saying this because we use, for example, the homogeneous  
> electron gas model for LDA calculations, nonetheless it is still "ab- 
> initio".
> I think that it's not the use of parameters or models that define a  
> first principles method, but from where those parameters were taken.
> If your parameters came from experimental values, it's somewhat  
> empirical (or semi-empirical at least), if you used just theoretical  
> values (even if using a simplified model) it can be called ab-initio.
> Is this right?
> This can even create some discussion if some new functionals can be  
> called "ab-initio" or not...
> Leonardo Matheus
> IF-USP / Brazil
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Stefano Baroni - SISSA  &  DEMOCRITOS National Simulation Center -  
http://www.sissa.it/~baroni / [+39] 040 3787 406 (tel) -528 (fax) /  
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