# CCL:G: incremental and nonincremental Fock matrix

*From*: Simen Reine <simen.reine-*-kjemi.uio.no>
*Subject*: CCL:G: incremental and nonincremental Fock matrix
*Date*: Thu, 8 Mar 2012 14:04:32 +0100 (CET)

Sent to CCL by: Simen Reine [simen.reine_-_kjemi.uio.no]
Hi Reza,

`The Fock matrix F(D) consist of a one-electron, h, and a two-electron
``contributuion (that depends on the density-matrix D), G(D), accoring to
` F(D) = h + G(D).

`In the non-incremental Fock matrix scheme the full Fock matrix is
built in
``each SCF iteration, whereas in the incremental Fock matrix scheme the
Fock
``matrix is built by adding only the two-electron correction (or
increment)
``to the Fock matrix of the previous SCF iteration
` F(D) = F(D') + G(D'-D)

`where D is the current and D' the previous density matrix. The
incremental
``Fock matrix construction is typically much more efficient since the
``difference between the two densities is small - thus allowing for more
``efficient screening.
` Hope this helps!
On Thu, 8 Mar 2012, 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.
">
`

______________________________________________________________
Dr. Simen S. Reine, Researcher at the
Centre for Theoretical and Computation Chemistry (CTCC)
Department of Chemistry E-mail: simen.reine{=}kjemi.uio.no
University of Oslo Mobile ph.: (+47) 93 07 10 96
P.O.Box 1033 Blindern Telephone : (+47) 22 85 81 49
N-0315 Oslo, Norway Fax : (+47) 22 85 54 41
______________________________________________________________