CCL:G: Avoided crossing

 Sent to CCL by: "Abrash, Sam" [sabrash**richmond.edu]
 As far as I understand it, avoided crossings are always between states of the
 same symmetry, so there wouldn't be an avoided crossing between a singlet and a
 triplet state.
 Sam
 Samuel A. Abrash
 Department of Chemistry
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 -----Original Message-----
 > From: owner-chemistry+sabrash==richmond.edu%ccl.net [mailto:owner-chemistry+sabrash==richmond.edu%ccl.net] On Behalf Of Walid M.
 I. Hassan walid_m76.:.yahoo.com
 Sent: Thursday, April 19, 2012 7:37 PM
 To: Abrash, Sam
 Subject: CCL:G: Avoided crossing
 Sent to CCL by: "Walid M. I. Hassan" [walid_m76|-|yahoo.com]
 Dear Scientists
 long time since I send email via this list,
 my question is very simple does anyone know a software to determine the
 avoided crossing or conical intersection between singlet and triplet states,
 i mean states of different multiplicity
 In Gaussian 09 manual, in Opt keyword ,under conical option it is written,
 "Search for a conical intersection or avoided crossing using the state-
 averaged CASSCF method. Avoided is a synonym for Conical. Note that
 CASSCF=SlaterDet is needed in order to locate a conical intersection between
 a singlet state and a triplet state."
 I tried this and find it is impossible since in input file you determine a
 singlet or triplet multiplicity but not both
 and SlaterDet option just reverse the spin but do not change multiplicity
 see this part of output to see the configurations
 when I use singlet state with No SLATER DETERMINANT
 > I get the following configuration
 >        Configuration      1 Symmetry 1 111000
 >        Configuration      2 Symmetry 1 11ab00
 >        Configuration      3 Symmetry 1 110100
 >        Configuration      4 Symmetry 1 1a1b00
 >
 >
 > which become as follows with SLATER DETERMINANT
 >        Configuration      1 Symmetry 1 111000
 >        Configuration      2 Symmetry 1 11ba00
 >        Configuration      3 Symmetry 1 11ab00
 >        Configuration      4 Symmetry 1 1b1a00
 >        Configuration      5 Symmetry 1 11b0a0
 >
 >
 > for triplet state in both cases i get the following configuration
 >  Configuration      1 Symmetry 1 11aa00
 >        Configuration      2 Symmetry 1 11a0a0
 >        Configuration      3 Symmetry 1 1a1a00
 >        Configuration      4 Symmetry 1 110aa0
 as you can see SlaterDet option reverse ab to ba but not to aa
 I want to get conical intersection or avoided crossing between
 Configuration      1 Symmetry 1 111000 of singlet and
 Configuration      1 Symmetry 1 11aa00 of triplet state
 I sent this question to Gaussian team and their reply was not convincing to
 me, I will put it here for your reference,
 I think they just go around the problem to claim that there is no problem in
 the manual
 i think gaussian program can not do it
 if i am wrong i will appreciate if you guide me
 If i am write so what program can find this conical intersection for me
 sorry for long email but i think it won't show my point if it is shorter
    Dr. Ibrahim,
     Thank you for giving us a chance to comment.
     When you look at those configuration lists you are not actually
 looking a lists of identical things.  The singlet without Slater Determinant
 is a list of configurations, fixed linear combinations of determinants
 giving singlets.  So there will be no triplet terms in this expansion
 and the higher roots of the CASSCF equations will all be singlets as
 well.
     The second case lists determinants directly and generates singlets
 and m(l)=0 triplets.  So configurations 2 and 3 are a pair of determinants
 which can contribute to both singlets and triplets with the sign difference
 carried on the CI expansion coefficients, not on the determinants
 directly.
       The third case correspond to a ground state triplet, m(l)=+/-1
 and no singlet contributions are possible.  Again any excited states will
 be triplets so this reference is not suitable for the crossing.
       So the program can compute the crossing you desire by using a
 singlet reference with SlaterDet included in the option list.  You
 should still solve for the first few roots to confirm that you have
 the second root corresponding to the triplet you expected.http://www.ccl.net/cgi-bin/ccl/send_ccl_messagehttp-:-//www.ccl.net/chemistry/sub_unsub.shtmlhttp-:-//www.ccl.net/spammers.txt