Subject: Re: CCL:Guess on change in geometry

From: Konstantin Kudin <konstantin_kudin^at^yahoo.com>
Date: Wed, 6 Oct 2004 08:00:06 -0700 (PDT)

Matt,

 There could be a number of ways to get density for an updated
geometry.
Perhaps, the easiest ones would be to purify the previous density
matrix, or diagonalize the old Fock matrix with the new orbitals. The
geometry changes should not be too large.
Specifically:

1) density purification -
 Diagonalize {-SV*D*(SV)^t} where D is the old atomic density, S, V are
new overlap and orthonormal basis coefficient matrices. Occupy Ne
lowest eigenvalues. That is what {-} is for. With the {-}, 1 becomes -1
and everything is sorted by the diagonalization routine itself.

2) old Fock diagonalization -
 Diagonalize {V^t*F*V}, where F is the old Fock matrix, V is a new
orthonormal coefficient matrix. As before, occupy Ne lowest
eigenvalues.

 {^t} stands for complex-conjugate.

 My experience would suggest that 1) appears to be better than 2),
although if the gain is significant or marginal I am still not fully
sure.

 I have used 2) a lot with the periodic boundary conditions
calculations. On the other hand, 1) worked like a charm when I needed
to create a good density matrix from ionic densities, then D consisted
of patches for ionic densities with 0s for cross-ionic density
elements. Such "patching" permits one to keep the ionic electronic
state for transition metals.

 Kostya

--- Matt Challacombe <MChalla^at^ICE.LANL.GOV> wrote:

> Hi,
> 
> I haven't seen much in the quantum chemistry literature on methods
> for 
> creating a new guess to start an SCF after a change in geometry.  I'm
> guessing
> this is something that most code developers take for granted, and
> never really
> publish.  Do any of you CCL'ers out there have the intimate details
> of these
> procedures for your code of choice?  
> 
> Thx, Matt
> 
> -- 
> Matt Challacombe, Group T-12, LANL
> MChalla^at^LANL.Gov, (505) 665-5905
> http://www.t12.lanl.gov/~mchalla/
> 

_______________________________
Do you Yahoo!?
Declare Yourself - Register online to vote today!
http://vote.yahoo.com