CCL:G: Energy convergence around conical intersection

[Wai-To Chan <chan__curl.gkcl.yorku.ca>]

 Sent to CCL by: Wai-To Chan [chan]^[curl.gkcl.yorku.ca]
    When running into convergence difficulites with CASSCf using GAMESS
 I would turn on the second order method as set by FULLNR=.TRUE.
 in $MCSCF. This method is considerably more time consuming than
 the default method.
    My experience is that what affect convergence most is the initial
 guess you use. For open shell systems I always stick with Pulay's
 procedure of using UHF-UNO. This procedure can be difficult for
 partial biradicals which requires you to obtain a broken spin-symmetry
 solution for a closed shell system. The stable=opt option in Gaussian
 might help if you know how to import the stable UHF solutions to GAMESS.
 I once considered this option but gave up later. Usually it just takes
 some extra effort to 'teach' GAMESS to produce the same stable UHF
 solution obtained from Gaussian by experimenting with various options.
 The extra work always pays off as GAMESS has far superior CASSCF
 convergence capability.
    I assume you are running energy calculations not geometry
 optimization. I believe GAMESS can only do MCSCF calculation
  of the energy gradient of a pure state.
 Wai-To Chan
 <<<<<<<<<<<<<<<<<<<<<<
 Sent to CCL by: "Sherin   Alfalah" [shireen.alfalah-*-yahoo.com]
  Dear CCL users,
  We are trying to run energy calculations for some points around a conical
  intersection. I am facing some problems in convergence for the excited state.
 To
  reach MCSCF convergence, we try to read some molecular orbitals of other close
  points or to run the energy calculations for the excited state with more weight
  of the ground state for example "0.1 or 0.2". In the conical
  intersection region, reading different vectors may lead to different stationary
  points with different energies.  I am a bit confused about the most proper way
  to have convergence. Shall it be the choice of method that gave the lowest
  energy or what? How can I know that I am not over shooting the minimum?
  We are using GAMESS, I am wondering if the results we have are due to chemical
  reasons or some artificial results of GAMESS software.
  I think that having more weights of the ground state, is reasonable since the
  points are within the conical intersection area?
  I am wondering about the most proper way to obtain convergence? and also if
 some
  one has any experience or know some tricks that may be useful to obtain
  convergence? Also, any information or discussion for this issue would be highly
  appreciated.
 >>>>>>>>>>>>>>>>>>>>>>>..