Re: CCL:G:[Q]: How to keep a particular state in G94?



 yu (yu-: at :-infiniti.wavefun.com) wrote (Wed, 15 Nov 1995 07:57:54 -0800):
 > On Nov 15, 11:29am, <bcnlma-: at :-hkpucc.polyu.edu.hk> wrote:
 > > Subject: CCL:G:[Q]: How to keep a particular state in G94?
 > > Dear all,
 > >
 > > I had a question that I hope someone on the list can help. I am
 > > doing some calculations on small transition metal compound using
 Gaussian
 > > 94. I carried out an SCF calculation which gives me a particular state
 but
 > > I would like to calculate a DIFFERENT state. After using
 > > guess=(read,alter) to get to the state I like, the SCF brings it back
 to
 > > the original state that I do not want.
 > >
 > > My question is: is there anyway I can get Gaussian to keep the same
 > > state from my guess=(read,alter) job?
 > >
 > > yours sincerely,
 > > Ida N. L. Ma
 > >
  ...
 >
 > Dear Dr. Ma,
 >
 > The reason causing your problem isn't program you used, but a basic
 theoretical
 > one. If the excited state you want to get has same symmetry with ground
 state,
        ========================================================================
 > according to the Variational Principle (SCF bases on the principle), if you
                                                                        ======
 > only do One-Determinant calculation, the energy you get is always the
 ground
   ============================================================================
 > state's. To study your problem, you need to use MCSCF or sophisticated CI
   =======
 > methods.
 >
 > Good luck!
 >
 > Jianguo Yu
 >
 Is the underlined sentence really true? As far as I remember the
 excited states of the same symmetry as the ground state are saddle
 points of the functional that is minimized in a variational calculation
 (as are the excited states of the other symmetries). That would imply
 that an SCF calculation can converge to a particular excited state of
 ground state symmetry if the initial guess is close enough.  (in
 principle, not paying attention to rounding errors etc.)
 I faintly remember that some people did a similar thing in DFT to
 obtain excited states from one-determinant wave functions.
 If this saddlepoint approach is in principle ok, the main problem would
 be to get accurate initial guesses. In a situation where many excited
 states are close together in energy or closely coupled (like in many
 transition metal compounds), this is expected to be rather difficult.
 By the way: The above should not be interpreted in the sense that I
 recommend not to use MCSCF / CI.  8^)
 Best regards
 Herbert Homeier
 --------------------------------------------------------------
 Dr. Herbert H. H. Homeier
 Institut fuer Physikalische und Theoretische Chemie
 Universitaet Regensburg
 D-93040 Regensburg, Germany
 Phone: +49-941-943 4720                FAX  : +49-941-943 2305
 email: na.hhomeier-: at :-na-net.ornl.gov
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