On Mon, Jul 28, 2008 at 07:20:54PM -0430, Muammar El Khatib wrote: > Are you sure about this? I mean as far as I have studied, DFT is not > considered > as Ab Initio (some people say yes, others no). Maybe calculation quality is as > good as Ab Initio (DFT takes care about electronic correlation) but DFT starts > from the premise that the electronic density is taken as the basic quantity. > So > the electronic density is the function taken for the functional (in this case > the energy) while Ab Initio (like Hartree - Fock for instance) are based on > the > many-electron wavefunctions. On the other hand DFT uses parameters derived > from > _empirical data_, or from more complex calculations and in that moment is when > DFT does not follow the "calculations from first principles" (where no > empirical > data is used).
While you certainly have valid points concerning the classification of DFT vs. other methods from a scientific POV, what matters at hand is the classifaction for the user who wants to use Debian to do stuff. And at this level, DFT (at least talking from a computational chemistry point of view here) is identical to other ab-inito methods like MP2 or CCSD. Besides, how many empirical parameters you have depends on the particular exchange-correlation functional you use, in theory I think one can construct those functionals without using empirical parameters (see e.g. the PBE functional, Phys. Rev. Lett., 77, 3865). The very popular B3LYP functional indeed has a couple of them, but stil in this case you are doing an all-electron calculation if you choose so. The devide here is between ab-initio and semi-empirical - where the latter has a whole different dimension of empirical parameters it uses, and this is the useful destinction for users. cheers, Michael -- To UNSUBSCRIBE, email to [EMAIL PROTECTED] with a subject of "unsubscribe". Trouble? Contact [EMAIL PROTECTED]
