CCL:G: [SPAM] CCL:G: RI DFT approximation in G03
- From: frisch|a|gaussian.com (Michael Frisch)
- Subject: CCL:G: [SPAM] CCL:G: RI DFT approximation in G03
- Date: Wed, 8 Mar 2006 10:40:18 -0500
Sent to CCL by: frisch[*]gaussian.com (Michael Frisch)
On Wed, Mar 08, 2006 at 09:07:06AM -0500, Stefan Grimme grimmes..uni-muenster.de
> Sent to CCL by: Stefan Grimme [grimmes---uni-muenster.de]
> Dear Pablo,
> for acetone PBE/SV(P) I get a RI-non-RI difference of
> 0.6 mEh with TURBOMOLE (old Coulomb aux-basis).
> Some time ago I did a RI-test with G03 that also produced a very, very big
> difference of some hundreds of mEh, so to me that sounds like a program
The way the coefficients for contracted fitting sets are specified in
G03 is rather eccentric and accounts for this problem. You have to
provide the coeficients of the unnormalized primitives, which is
The easiest way to use density fitting in G03 is to use the option to
automatically generate the fitting set from the AO basis, e.g.
HCTH/TZVP/Auto if you prefer the Alrichs basis sets.
The automatically generated set gives similar accuracy to the Alrichs
fittings sets for energies. Geometries and frequencies are virtually
identical to the non-fitted results -- the differences are much, much
smaller than the errors inherent in the method. So if you're doing a
study using a pure DFT functional in G03, you should routinely use
/Auto rather than doing the Coulomb problem without fitting.
Fitting also speeds up TD-DFT with pure functionals. TD-DFT results are
a lot better with hybrid functionals, but for medium to large molecules
it's often faster to do the pure calculation first as a guess for the
B3LYP/Aug-CC-pVTZ TD=Read Geom=Check Guess=read