Re: [Wien] Ab inition and DFT
Hello, Maybe the difference you are referring to is that between what theoretical chemist consider as "ab initio" and what physicists do. This was a matter of controversy in the 1990’s, and to me, is more philosophical that physical. For theoretical chemist, ab initio methods are methods based on the wavefunction, namely Hartee-Fock, and post-Hartree-Fock techniques (e.g., CAS-MCSCF, coupled cluster, CISD, Full-CI). In this sense, DFT is not ab initio as the main ingredient of DFT is the electron density, which is obtained from an approximate description of XC interelectronic interactions. For physicists DFT is ab initio as the method is grounded on a theorem (HK one) and "starts from scratch". Final note: for Walter Kohn, DFT is ab initio, not a semi-empirical methods (as many people coming from the community of theoretical chemists used to claim in the 1990’s), but its usage (LDA, GGA,…) is "something else » (if I remember well he said "it is just physics », [of interelectronic interactions]), as it relies on approximations in the XC functionals. Today, this controversy has been shelved, and everybody, as far as I could see, use indiscernibly DFT or ab initio. Best, Pascal > Le 7 juil. 2022 à 13:59, Fecher, Gerhard a écrit : > > This is an unsuitable question, you ask what is the difference between > "from the beginning" and "density functional theory" > > probably one can speculate whether you might mean > " What is the difference between "Hartre Fock", "Hohenberg Kohn", and "Kohn > Sham" theoretical approaches to the elecstronic structure of atoms, > molecules, or solids?" > In that case, a good textbook or the original works might help you the > latter rather better than second hand multiple genealogy references ==> do > your study ab initio ! > > Ciao > Gerhard > > DEEP THOUGHT in D. Adams; Hitchhikers Guide to the Galaxy: > "I think the problem, to be quite honest with you, > is that you have never actually known what the question is." > > > Dr. Gerhard H. Fecher > Institut of Physics > Johannes Gutenberg - University > 55099 Mainz > > Von: Wien [wien-boun...@zeus.theochem.tuwien.ac.at] im Auftrag von ben amara > imen [imen.benama...@gmail.com] > Gesendet: Mittwoch, 6. Juli 2022 15:18 > An: w...@theochem.tuwien.ac.at; wien@zeus.theochem.tuwien.ac.at > Betreff: [Wien] Ab inition and DFT > > 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 > ___ > Wien mailing list > Wien@zeus.theochem.tuwien.ac.at > http://zeus.theochem.tuwien.ac.at/mailman/listinfo/wien > SEARCH the MAILING-LIST at: > http://www.mail-archive.com/wien@zeus.theochem.tuwien.ac.at/index.html Pascal Boulet — Professor in computational materials chemistry - DEPARTMENT OF CHEMISTRY University of Aix-Marseille - Avenue Escadrille Normandie Niemen - F-13013 Marseille - FRANCE Tél: +33(0)4 13 55 18 10 - Fax : +33(0)4 13 55 18 50 Email : pascal.bou...@univ-amu.fr <mailto:pascal.bou...@univ-amu.fr> smime.p7s Description: S/MIME cryptographic signature ___ Wien mailing list Wien@zeus.theochem.tuwien.ac.at http://zeus.theochem.tuwien.ac.at/mailman/listinfo/wien SEARCH the MAILING-LIST at: http://www.mail-archive.com/wien@zeus.theochem.tuwien.ac.at/index.html
Re: [Wien] Ab inition and DFT
This is an unsuitable question, you ask what is the difference between "from the beginning" and "density functional theory" probably one can speculate whether you might mean " What is the difference between "Hartre Fock", "Hohenberg Kohn", and "Kohn Sham" theoretical approaches to the elecstronic structure of atoms, molecules, or solids?" In that case, a good textbook or the original works might help you the latter rather better than second hand multiple genealogy references ==> do your study ab initio ! Ciao Gerhard DEEP THOUGHT in D. Adams; Hitchhikers Guide to the Galaxy: "I think the problem, to be quite honest with you, is that you have never actually known what the question is." Dr. Gerhard H. Fecher Institut of Physics Johannes Gutenberg - University 55099 Mainz Von: Wien [wien-boun...@zeus.theochem.tuwien.ac.at] im Auftrag von ben amara imen [imen.benama...@gmail.com] Gesendet: Mittwoch, 6. Juli 2022 15:18 An: w...@theochem.tuwien.ac.at; wien@zeus.theochem.tuwien.ac.at Betreff: [Wien] Ab inition and DFT 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 ___ Wien mailing list Wien@zeus.theochem.tuwien.ac.at http://zeus.theochem.tuwien.ac.at/mailman/listinfo/wien SEARCH the MAILING-LIST at: http://www.mail-archive.com/wien@zeus.theochem.tuwien.ac.at/index.html
Re: [Wien] Ab inition and DFT
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___ Wien mailing list Wien@zeus.theochem.tuwien.ac.at http://zeus.theochem.tuwien.ac.at/mailman/listinfo/wien SEARCH the MAILING-LIST at: http://www.mail-archive.com/wien@zeus.theochem.tuwien.ac.at/index.html
[Wien] Ab inition and DFT
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 ___ Wien mailing list Wien@zeus.theochem.tuwien.ac.at http://zeus.theochem.tuwien.ac.at/mailman/listinfo/wien SEARCH the MAILING-LIST at: http://www.mail-archive.com/wien@zeus.theochem.tuwien.ac.at/index.html
