Subject: electric field + H2+ SUMMARY

From: "Nguyen N. Anh" <[email-masked]>
Date: Thu, 20 May 1999 03:12:57 -0400

Dear cclers,

Some days ago I posted a question concerning calculations of resonance states
using quantum chemical codes. Since then I've got 2 responses and some requests
for summarizing. One of the references I got seems to be very relevant and it
helps me very much. ( Chao, Falcetta, Jordan, JCP, 93, 1125). I realized that
resonance states calculations are difficult, but sufficient effort is being
made to do it, in particular by using electronic structure programs.

Thanks to all who responded and who were interested in my posting

Best regards

Nam-Anh Nguyen

-------------------

> Dear cclers,
>
> I'm doing very "simple" abinitio calculations on the H2+ molecular system
using
> g94. A strong electric field has been applied (using Field keyword) which
> distorts the original Coulomb potential of the molecule, i.e. a linear
> potential is added to the Coulomb one. Thus the molecule's LUMO and HOMO can
> interact with continuum states of the linear potential of the electric field
to
> form resonant states, and electron can tunnel out.
>
> The difficulty is: to generate correct resonant states, we have to provide
> basis sets that can support continumm states of the electric field. Standard
> Gaussian basis sets centered at the H atoms alone are not sufficient.
>
> My question: Does anyone know of any similar abinitio calculation? Or any
basis
> set that supports continuum states?
>
-------------------
>From Dr. Falcetta:
Hi,

I am not sure that I exactly understand your question, but I might have an
approach that could help.  Are you trying to find the resonant states of H2+
with respect to ionization (ie to form H2++) in the presence of a strong
electric field

on approach to introducing a continuum/resonant resolution using standard
quantum chem codes is the stabilization method.  Dr K. D> Jordan and I have
done several calculations using this approach.  We include several diffuse
gaussian basis functions in the atomic basis set and do several calculations
each
calculation is different in that the exponents of the diffuse functions are
scaled by multiplication by a constant.  The eigencalues (you need to extract
several) are plotted as a function of this scaling parameter.  If you need the
lifetimes as well you need to a bit more math.  Two references, if this sounds
promising: chem phys letter vol 300 page 588 and JCP vol 93 1125.

I am really not sure that this is relevant because I am not quite clear on the
exact problem.  But if I can be of help you can e-mail me

good luck

Mike Falcetta

------------------
>From Dr. Valerio
Hi,

of course localized basis set cannot describe the ionized free electron,
which is well represented by a plane wave. I am aware of theoretical
studies on atoms only and I can suggest you the following refernces:

H.A. Bethe, E.E. Salpeter, it Quantum Mechanics of One- and
Two-Electron Atoms (Springer-Verlag 1957).

L.D. Landau, E. M. Lifshitz, Quantum Mechanics.

and this recent paper:

D. Fisher, Y. Maron, L.P. Pitaevskii, Phys. Rev. A {\bf 58},
2214 (1998).

I hope it helps
Best regards

                        Gabriele

--------------

-- 
Nguyen Nam Anh   Quebec, Canada
E-mail: [email-masked]
WWW: http://promethium.chm.ulaval.ca/~anh/