Thiophene has 6 pi electrons, and I would assume that
the bithiophene
you have has 12 pi electrons... This doesn't answer the CASMP2 issue,
however.
John McKelvey
On 5/15/07, *Ulrike Salzner salzner++fen.bilkent.edu.tr*
<owner-chemistry^ccl.net <mailto:owner-chemistry%5Eccl.net>> wrote:
Sent to CCL by: Ulrike Salzner [salzner^-^fen.bilkent.edu.tr
<http://fen.bilkent.edu.tr>;]
Hello,
while trying to calculate the excitition energies of the bithiophene
dication with CASMP2 using Gaussian 03 I ran into the following
problem.
I am using all of the pi-electrons and pi-orbitals (10 electrons
and 10
orbitals). I got the ground and 5 excited states at the CASSCF level
without problems. Then I tried CASMP2 with the same active space.
First
there is a warning that there are more than 10000 configurations,
there
are actually about 63504. In the MP2 part all confuguratons are
skipped
and then it prints:
"Multireference MP2 with 0 configurations"
and the energy is same as without MP2. The same happens for ground and
first excited state. What is the problem? Is the active space too
large?
After reducing the active space to (8,8), MP2 runs using 21
configurations.
How are the configurations selected? How reliable is such a
result? Will
it use more configurations, if I reduce the active space further?
Thanks for assisstance,
Ulrike
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