Re: CCL:G:G94: B3LYP energy and Charge



 Mike Frisch writes:
   >
   > > The answer is that both are right!  The Gaussian definition of B3LYP
   > > uses the VWN local correlation functional;  most other programs use
   > > what Gaussian terms VWN5.
   > >
   >
   > No, B3LYP was defined to use VWN3.  Using the same name for two different
   > functionals is a disservice to everyone and makes reproducing other
 peoples
   > results impossible.  This used to be a major problem in the DFT area, and
   > things are finally improving with regard to terminology.  To take a name
 for
   > something that is specified in the literature and use it for something
   > different is a major step backwards.  Published and in-press tests of
 B3LYP
   > all use VWN3; an assumption that the same conclusions apply to a
 different
   > functional just because it has the same name are not valid.
   >
 Point taken.  All that I was implying in my original answer was that there
 are no 'numerical' problems here - both programs are giving correct results
 within their own definitions of B3LYP.  Most programs (such as Mulliken,
 CADPAC, MOLPRO, Turbomole) use the VWN5 functional uniformly as the
 local correlation part of functionals such as SVWN, B3P86 and B3LYP.  It
 is unfortunate that Gaussian is alone in using an alternative VWN local
 correlation functional and (as Mike says) that the terminology is not
 consistently defined.  The issue is further confused by a bug in the
 Gaussian 92/DFT open-shell VWN5 code which leads to small discrepancies
 with the other programs even when extremely large quadrature grids are
 used.
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 | Dr Ross Nobes                                                  |
 | Senior Scientist, Quantum Mechanics                            !
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