CCL:G: Energy convergence around conical intersection
- From: Wai-To Chan <chan__curl.gkcl.yorku.ca>
- Subject: CCL:G: Energy convergence around conical intersection
- Date: Sun, 10 Sep 2006 19:49:53 -0400 (EDT)
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
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.
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.
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
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