Subject: Excimer details

From: [email-masked] (Rovshan G. Sadygov)

Hellow Dear Netters,

Yesterday I posted a quiestion about excimer calculations. Thanks for
interest it brought about from some of you. People asked about details
of calculations and objectives. They are following;

I want to calculate excimer states of naphthalene dimer in parallel
conformation using supermolecule model of dimer. I need to find out
dependence of total energy of supermolecule on interplanar distance between
naphthalene monomers. Excited state of supermolecule corressponding to
HOMO->LUMO transition supposedly forms bound state at interplanar distance
3.3 - 3.5 A.
I also need to calculate second excited state of supermolecule. This state
is expected to be nonbonding, laying about 2.0 ev above excimer state at
bonding conformation of latter and approaching it at large interplanar
distances.

I have now a problem somehow close to one described by Dr T Bally in his
E-mail reply. 
According to Argus INDO1/s calcualtions ground state of supermolecule is
not repulsive at interplanar distances 2.0 - 3.0 A. As a matter of fact it
is attractive(!!!). 
MOPAC5 with AM1 Hamiltonian yields quite resonable results for ground state
of supermolecule. It predicts vdWaals bonding at 5.5 A interplnar distance and
repulsive ground state at interplanar distance shorter than 4.0 A.
The second problem with Argus is that at short interplanar distances
molecular orbital carrying LUMO features (which is antibonding) becomes an 
occupied molecular orbital in ground state. And conversely, MO corresponding
to HOMO of monomer becomes unoccypied MO. It is true for MOPAC5 AM1 too.

So these are problems I currently encounter in excimer calculations. 
I'll be glad to provide more details if needed.
Thanks in advance to all who are interested.

Rovshan G Sadygov.

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