*From*: Seth Olsen <s.olsen1[A]uq.edu.au>*Subject*: CCL: Energy convergence around conical intersection*Date*: Mon, 11 Sep 2006 10:49:49 +1000

Sent to CCL by: Seth Olsen [s.olsen1|a|uq.edu.au] Hi Sherin, Changing the weighting of the states in a state-averaged CAS calculation will give you convergence problems if the states are close together just because it doesn't take much variation in the energy of either state in order to flip the roots. I'm a bit confused as to what your objective is, though, since any weighting scheme other than 0.5/0.5 would be expected to overbias one state or the other. This would change the energy and the position of the intersection, and it's not clear to me that this would happen in a regular fashion. The question of what weighting is 'right' to describe the intersection (in the sense of getting the 'right answer for the right reason') does not seem to be very relevant because the 'right' weighting will probably vary depending on the state and the system. In this case, even if the 'right' answer is achieved, the weighting has become just a tuning parameter and its not clear that the it is 'right for the right reason'. When you vary the weighting, are you then comparing to something more trustworthy (like evenly-weighted MCQDPT or MRCI)? I've often thought that there isn't that information about state-averaging in the literature, given that it is the currently the most popular method for computational photochemical modeling. The rate of change of weighting of a state averaged CAS solution has been suggested as a diagnostic for the quality of the wavefunction (Stalring et al, Mol. Phys. v.2 pp.103-114 (2001)). In this work it is also pointed out that only for an evenly-weighted wave function is the final solution invariant to projections within the state-averaged subspace (in addition to the usual CASSCF orbital rotation invariance). This in turn has implications for the Lagrangian used to determine analytic gradients w/ respect to geometry. Good luck. :-) Cheers, Seth Sherin Alfalah shireen.alfalah^yahoo.com wrote:

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.Thanks in advance.**************************************Sherin AlfalahPhD StudentTheoretical ChemistChemistry DepartmentAlQuds University**************************************>