Subject: RE: CCL:Time-Dependent-DFT Oscillator Strengths

From: Nguyen Kiet A Contr AFRL/MLPJ <[email-masked]>
Date: Mon, 9 Aug 1999 15:47:12 -0400

I should have been more clear in my previous mail.  I wrote that TD-DFT
oscillator strength was not implemented UNTIL release A7.  So it is
implemented in A7 as Mike Frish has mentioned.  In previous releases the
oscillator strengths came straight out of the CIS codes.  This is not so
surprising since cisrho, a routine in l914 handles both CIS and TD-based
transition dipoles.  As far as I can tell Gaussian computes f (the length
form) using:

f = 2/3E(m(x)^2 + m(y)^2 + m(z)^2)
m(x) = Tr (MP)

P = Transition density matrix
M = transition dipole matrix
E = transition energy

Note: m(x), m(y), and m(z) in the G98 output are in au. So E must be
converted to au to get f in the formula above. 
 
The formulas are consistent with what I have seen in the literature.  It is
good to hear Mike Frish confirmed that implementation is correct.  Some of f
numbers I got from the program are in good agreement with experiment.
However, they are too small [in comparison to experiment and TDHF/INDOS
(this TDHF calculations using INDOS paramenters)] for the same molecule with
hydrogens being replaced by halogens using the same basis set.  This is
mainly why I was skeptical of the TD oscillator strengths from G98.
However, it is possible that halogens can drastically shift some of bands in
the spectrum that is not being revealed by room temperature experiment and
RPA/INDOS. 

Kiet Nguyen

> ----------
> From: 	Dr. Reinaldo Pis Diez
> Sent: 	Friday, August 6, 1999 3:03 PM
> To: 	Nguyen Kiet A Contr AFRL/MLPJ
> Subject: 	Re: CCL:Time-Dependent-DFT Oscillator Strengths
> 
> 	Hi Kiet,
> 
> 		I've found your posting to ccl very surprising. How did you
> noticed that
> the oscillator strength calculation was not implemented for td-dft in g98
> rev a7? It is strange that the program prints those values if it doesn't
> have them (correctly) implemented. 
> 		Regards,
> 
> 						Reinaldo
>