Subject: Non-Linear-Optics_and_MOPAC93

From: <[email-masked]>
Date: Wed, 8 Feb 95 17:00:57 -0600

Hi netters.

   One year ago (more or less) I posted a question about a strange behaviour
in MOPAC 93 when it is requested to calculate frequency-dependent NLO proper-
ties. This code use the TDHF equations and it is the same method implemented in
HONDO package (Karna S.P., Dupuis M., J. Comp. Chem, vol.12,p.487,(1991)).

The method is able to calculate the frequency-dependent values up to the first
pole (i.e. the homo-lumo gap). If I'm investigating a Second Harmonic
Generation effect, it means that the fundamental perturbating frequency can't
go beyond half the gap; if I'm investigating a Third Harmonic Generation
effect, it can't go beyond 1/3 gap.
An example of such a calculation is shown in  Karna S.P., Prasad P.N, Dupuis
M,  J. Chem. Phys. 94  1171  (1991). Calculations were carried out with the
ab-initio code HONDO.

I've tried to run MOPAC93 with the same molecule (p-nitroaniline) and I still
got strange results. Strange means out-of-format numbers... 
The calculated homo-lumo gap is between 8.2 and 8.4 eV (it depends on the
semiempirical methods, AM1, MNDO or PM3), but i get a "resonance" at 1.7 eV
of fundamental frequency for a SHG effect and at 1.2 eV for a THG effect.
Karna, Prasad & Dupuis have been able to calculate with TDHF equations SHG
>from 0 to 1.786 eV and THG from 0 to 1.494 eV of fundamental frequency.
One year ago I had similar problems in calculating NLO dispersion for fullere-
nes. The value at w=0.65 eV for SHG in C70 was absolutely meaningless (i.e.
very different from zero).

I would like to know if anybody else have faced (or is fighting with) the same
problem AND/OR if you are aware of referencies, people using MOPAC93-TDHF to
get frequency-dependent non-linear tensors AND/OR whatever you guess could help
me.

I will post a summary if I receive some answers. 

Many thanks.

Marianna

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      MARIANNA  FANTI
PhD Student
Dept. of Chemistry
207 Pleasant street  S.E
University of Minnesota
Minneapolis, MN 55414
Minnesota, USA

e-mail: [email-masked] 
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