Summary:**** Fatal Problem: The largest alpha MO coeffient is 0.12116834D+04



Dear all,
 On 28 Dec, I wrote:
 > Dear netters,
 >
 >       When I used g94 to perform a mp2 optimization on the molecule:
 > 1,3-buta-diyne. I got the error message shown in the title.
 >       Similarly, when I performed a CIS calculation on the same molecule, a
 > similar error  result.
 >       Any help and advice will be highly appreciated.
 >       Thanks in advance.
 >
 >
 > Best Regards,
 >
 >
 	Thank you very much for those give very helpful advises to above
 problem. They are summarized as follows:
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 From: "Han Young-Kyu" <ykhan.,at,.qcl.t.u-tokyo.ac.jp>
 Hello. I read your CCL. The problem  originates from the linear dependency
 of the basis sets you used. The problem has nothing to do with the methods such
 as CIS and MP2. Please check the basis sets.
 All the best,
 Han
 ***************************************************************
 Young-Kyu Han (Ph.D. Korean)
 Department of applied chemistry, Graduate school of engineering,
 The university of Tokyo, Hongo 7-3-1 Bunkyo-ku, Tokyo 113-8656,
 Japan
 Phone(or Fax) : +81-3-5841-7243(Lab)
 Email : ykhan.,at,.qcl.t.u-tokyo.ac.jp or ykhan.,at,.orbit.kaist.ac.kr
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 From: Christoph.van.Wuellen.,at,.ruhr-uni-bochum.de
 Such large MO coefficients can only arise if the overlap matrix has
 a very small eigenvalue. Perhaps something went wrong with the
 basis input?
 ---------------------------+------------------------------------------------
 Christoph van Wullen       | Fon (University):  +49 234 32 26485
 Theoretical Chemistry      | Fax (University):  +49 234 32 14109
 Ruhr-Universitaet          | Fon/Fax (private): +49 234 33 22 75
 D-44780 Bochum, Germany    | eMail:
 Christoph.van.Wuellen.,at,.Ruhr-Uni-Bochum.de
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 From: Karl Irikura <karl.irikura.,at,.nist.gov>
 Do you have diffuse functions in your basis set?  With the small C-C
 distances in your molecule, diffuse functions may give
 linear-dependence problems in the basis set.  Try deleting the most
 diffuse function from each C atom, or try a code that will delete
 functions automatically (e.g., Gaussian98, ACES II).
 I hope this helps--good luck!
 Karl I.
 ----------------------------------------------
 Dr. Karl K. Irikura
 National Institute of Standards and Technology
 100 Bureau Drive, Stop 8380
 Gaithersburg, MD  20899-8380
 voice: 301-975-2510     fax: 301-869-4020
 e-mail: karl.irikura.,at,.nist.gov
 http://www.nist.gov/compchem/
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 From: gaussian.com!csd.,at,.gaussian.com (Cust. Service Doug)
 When you have a near linear dependency in your basis set you can end up with
 very small eigenvalues of the overlap and very large values of MO coefficients.
 This can lead to serious numerical errors, especially for higher order
 correlated
 methods, so G94 prints an error message for coefficients greater than 100 and
 kill the calculation if it is greater than 1000.
 You can suppress this test by adding NoTestMO to the route.  Note that this
 option should be used with care and you need to monitor that the energy
 and other properties make sense.  I.e. compare MP2 energies with DFT to make
 sure the correlation energy is the right order of magnitude.  Higher order
 methods generally give smaller corrections at each order of correlation.
 --
   Douglas J. Fox
   Technical Support
   Gaussian, Inc.
   help.,at,.gaussian.com
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 Best Regards,
 Keung Lau