[Wien] Ab inition and DFT

[Gavin Abo]

You may want to go by how Karlheinz Schwarz describes them.

ab initio translates to "first principles" meaning no experimental data 
is needed and just physical constants can be plugged in to solve the 
theoretical equation.

The exact statement Schwarz uses in [1] is:

/The advantage of//first-principle (ab initio) methods lies in the fact 
that//they can be carried out without knowing any experi//mental data of 
the system. /

Wikipedia says [2]:

/Ab initio means "from first principles" or "from the beginning", 
implying that the only inputs into an ab initio calculation are physical 
constants./

DFT (Density Functional Theory) means a quantum mechanical model were a 
many-body problem can be solved using a density functional.

The exact statements Schwarz uses in [3] are:

/In this way DFT is a universal approach to the quantum mechanical 
many-body problem, where the system of interacting electrons is mapped 
in a unique manner onto an effective non-interacting system that has the 
same total density./

/According to DFT all that is needed is the density ρ(r) which only 
depends on the position r, i.e. on three coordinates./

Wikipedia uses the words:

/Using this theory, the properties of a many-electron system can be 
determined by using functionals, i.e. functions of another function. In 
the case of DFT, these are functionals of the spatially dependent 
electron density./

Based on the above, WIEN2k calculations can be both DFT and ab initio.

For further details, see Schwarz's publications [1,3] or you may look at 
other explanations you might find in a textbook or on the Internet such 
as [5,6].


[1] https://doi.org/10.1016/S0022-4596(03)00213-5
[2] https://en.wikipedia.org/wiki/Ab_initio_quantum_chemistry_methods
[3] http://dx.doi.org/10.5772/59108
[4] https://en.wikipedia.org/wiki/Density_functional_theory
[5] https://dft.uci.edu/doc/g1.pdf
[6] 
http://ccl.net/chemistry/resources/messages/1995/05/17.001-dir/index.html

Kind Regards,

Gavin
WIEN2k user

On 7/6/2022 7:18 AM, ben amara imen wrote:
> Dears users
>
> Can someone please  explain the difference between ab initio 
> calculation and DFT.
>
> As I know , ab initio calculation is based on wave function without 
> any empirical parameters . DFT is based on density of charge but it 
> uses the empirical parameters (within Exchange-correlation potentiel 
> PBE , GGA..).
>
> Is it correct ?.
>
> If it is correct , why some papers consider DFT as ab initio calculation.
>
> Thanks
>
>
> Best regards
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://zeus.theochem.tuwien.ac.at/pipermail/wien/attachments/20220707/d98bdb6c/attachment.htm>