Subject: The PM3 calculations for stilbens.

From: platonov <[email-masked]>
Date: Fri, 27 Mar 1998 16:39:57 +0300

Dear collegues!
       We study electronic properties in a range of
perfluorstilbens - C6H5-(CF2=CF2)n-C6H5 by means of
polarography  and  half-empyrical quantum chemistry
methods such as PM3. In that range of fluor substi-
tuted stilbens the correlation  bitwin  numbers  of
-CF2=CF2- bridges (between two benzene cycles)  and
value of  E(homo)-E(lumo)  was observed, the latter
value  being  calculated  using  RHF/PM3  method in
HYPERCHEM 4 (Hypercube Inc.) for windows.  Unfortu-
nately we can't acquire any good correlation  using
the same method in GAUSSIAN-94.  We  took  Z-Matrix
>from hyperchem optimized geometry for each substan-
ce  translated  it  to  input file for GAUSSIAN-94,
specifing in it neccesarible route section and then
perform geometry optimization in GAUSSIAN-94.
            Route section example:
# RHF/PM3 Guess=Huckel FOpt=(Z-Matrix, VTight)
# Pop=Reg SCF(Conver=10)
       In addition to it the final optimized geomet-
ries for the same substance in Hyperchem  and  Gaus-
sian is quite different from one another. The Hyper-
chem obtained final geometry  is  absolutely  planar
for all members of represented range  (n=1-6)  while
Gaussian obtained geometry is planar only for  C6H5-
CF2=CF2-C6H5 (n=1). Another  molecules  were twisted
around axis that combines centres of benzene cycles.
       Please  explain me why  this  phenomena  take
place?  If  you need in more substantial information
let me know about it.
Thank you.

Sincerely Yours D. Platonov.
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º           Dmitrii V. Platonov - postgraduate student           º
º  Moscow Lomonosov State Academy of Fine Chemical Technology.   º
º                   117571, Moscow, Russia                       º
º                   phone: (095)515-24-37                        º
º               e-mail:[email-masked]                    º
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