Re: CCL:Defining orbitals

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    Dr. Thompson,
     Doing excited states with MP2 is tricky.  The HF reference and the
 MP2 expansion are done with a single determinant and the SCF procedure
 solves for the lowest energy of a given point group symmetry.  For Li-
 atom you have nearly degenerate p orbitals, depending on the water(s)
 around this it will lift the degeneracy but it may also result in
 fewer than 3 symmetry distinct states.
     What might be a better approach is to look at TD-DFT which has
 some effect of correlation, not as good as MP2 for this case, but it
 will give you a spread of low energy excited state energies based on
 the ground state orbitals.  Pick one of the gradient corrected or
 hybrid functionals, B3LYP or B3PW86 are well studied, and a fairly
 large basis set including diffuse functions and polarization, 6-311+G(d,p)
 or better, and see what you get.
    If you do have some symmetry you can generally use Guess=(Read,Alter)
 to flip occupancy and get different states for the MP2 approach.
 On Tue, Jun 14, 2005 at 11:46:04AM +1000, Christopher Thompson wrote:
 > David,
 >
 > You interpreted my question correctly. Without going into the
 > experiment in detail ... we generate Li-(H2O)n clusters and record
 > their infrared spectrum. The source of Li- can potentially create Li-
 > anions in more than the lowest energy singlet state. It appears that
 > the symmetry of the clusters is not the same for different e spin
 > states on the Li- ... an excellent way to differentiate species in
 > vibrational spectroscopy. It would be nice to characterise the
 > different triplet states comprehensively.
 >
 > Cheers,
 > Chris
 >
 > On 14/06/2005, at 3:40 AM, Shobe, David wrote:
 >
 >
 > > Yes, but...I think he wants to study what would more correctly be
 > > called a particular state of Li anion triplet.
 >
 > >
 > >
 > > I don't remember how Gaussian treats the degeneracy of the three p
 > > orbitals.  If Gaussian just arbitrarily picks one of the three p
 > > orbitals, no special manipulation is needed; but if the HOMO is a
 > > mixture of px, py, and pz it's a different story...
 >
 > >
 > >
 > >
 > > --David Shobe, Ph.D., M.L.S.
 >
 > >
 > > S|d-Chemie, Inc.
 >
 > >
 > > phone (502) 634-7409
 >
 > >
 > > fax (502) 634-7724
 >
 > >
 > >
 > > Don't bother flaming me: I'm behind a firewall.
 >
 > >
 > >
 > > From: Computational Chemistry List
 > > [mailto:chemistry-request = = = ccl.net] On Behalf Of Wayne Steinmetz
 >
 > >
 > > Sent: Friday, June 10, 2005 4:46 PM
 >
 > >
 > > To: chemistry = = = ccl.net
 >
 > >
 > > Subject: CCL:Defining orbitals
 >
 > >
 > >
 > > The electrons belong to the entire atom and are not constrained to
 > > any orbital.  One uses orbitals to construct the wave function.
 > > One must be sure that the set of orbitals, i.e. the basis set, is
 > > sufficiently flexible to describe completely the molecular species.
 > >  You are dealing with an atomic species so a polarization basis
 > > set is probably not needed.
 > >
 > > Wayne E. Steinmetz
 > > Carnegie Professor of Chemistry
 > > Woodbadge Course Director
 > > Chemistry Department
 > > Pomona College
 > > 645 North College Avenue
 > > Claremont, California 91711-6338
 > > USA
 > > phone: 1-909-621-8447
 > > FAX: 1-909-707-7726
 > > Email: wsteinmetz = = = pomona.edu
 > > WWW: pages.pomona.edu/~wsteinmetz
 > >
 > > -----Original Message-----
 > > From: Computational Chemistry List
 > > [mailto:chemistry-request = = = ccl.net] On Behalf Of Christopher
 > > Thompson
 > > Sent: Thursday, June 09, 2005 6:09 PM
 > > To: chemistry = = = ccl.net
 > > Subject: CCL:Defining orbitals
 > >
 > > Gday,
 > >
 > > I would like to do an MP2 calc on a Li- species in triplet state.
 > >
 > > With one electron in the s orbital and one in a p orbital,
 > > how can you constrain the electron to say the px orbital?
 > >
 > > Cheers,
 > > cdth = = = unimelb.edu.au
 > >
 > > Christopher Thompson
 > > Laser Spectroscopy Group
 > > School of Chemistry
 > > University of Melbourne
 >
 > >
 > >
 > Dr Christopher Thompson
 > Laser Spectroscopy Group
 > School of Chemistry
 > University of Melbourne
 > VIC, Australia, 3010.
 > Ph. +61 3 8344 8163
 > Fax. +61 3 9347 5180
 >
 >
 --
 Douglas J. Fox
 Technical Support
 Gaussian, Inc.
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