# CCL:G: incremental and nonincremental Fock matrix

*From*: Heribert Reis <hreis- -eie.gr>
*Subject*: CCL:G: incremental and nonincremental Fock matrix
*Date*: Thu, 08 Mar 2012 15:26:00 +0200

Sent to CCL by: Heribert Reis [hreis###eie.gr]
Dear Reza,
NoIncFock calculates the Fock-matrix from scratch at each SCF step,
which is expensive, but accurate.
IncFock approximates the Fock-matrix by adding up the changes due to the
density matrix change from consecutive steps of the SCF:
F(P_i) = F(P_i-1) + F(P_i - P_i-1), where P is the density.
This is faster than NoIncFock, and the approximation is a good one, if
the density changes are small, e.g. close to convergence, but may also
fail.
Heribert
On Thu, 2012-03-08 at 05:45 -0500, Reza Shojaei shojaei81[A]gmail.com
wrote:
> Sent to CCL by: "Reza Shojaei" [shojaei81%%gmail.com]
> Dear all,
>
> Do you have any idea about the exact meanning of incremental Fock matrix
which is default setting for direct SCF.
> What's the non incremental fock matrix?
> here I put the Gaussian's manual which I don't understand:
> "IncFock:
> Forces use of incremental Fock matrix formation. This is the default for
direct SCF. NoIncFock prevents the use of incremental Fock matrix formation, and
it is the default for conventional SCF. ">
>