[Pw_forum] ab initio vs. first principles.
davidfarrell2008 at u.northwestern.edu
Mon Dec 22 03:09:19 CET 2008
I also had a similar question in my head for a while about the
ubiquitous use of ab initio == quantum mechanical model in materials
science and physics literature (nanomechanics as well, for what it's
worth). Mostly because some of the techniques include things that are
definitely approximations or involve some sort of parameterization.
Now, compared to empirical potentials, DFT, Hartree-Fock and even many
Tight Binding approaches are certainly 'ab initio' because of how and
where the approximations are made... and this seems to be the
justification for using 'ab initio' in this manner. Besides, it sounds
cool when written or said... a reason whose influence probably
shouldn't be underestimated.
On Dec 21, 2008, at 7:47 PM, 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-
> 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
> Pw_forum mailing list
> Pw_forum at pwscf.org
David E. Farrell
Department of Materials Science and Engineering
email: d-farrell2 at northwestern.edu
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