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
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```