CCL:G: Gaussian Job

Gaussian has one of the best optimizers for QM.  Before trashing G09, make
 sure your structure is indeed correct chemically.
 Second, optimizing a structure at a lower level of theory and then
 re-optimizing at a higher level of theory often (not always) overcomes
 convergence issues wrt structure.
 Thirdly, your comments are ambiguous.  Do you mean to say that the
 wavefunction did not converge or that there were difficulties in getting a
 converged wavefunction?  Or do you mean the optimization did not converge?
 If the latter and there is not an issue with cpu time, why quit on Gaussian?
 If your issue is with the convergence of the wavefunction alone, then there
 is plenty on both the G09 web site and the CCL archives about approaches to
 dealing with unstable wavefunctions.
 If your system is pathogenic using G09 and wish to explore another program
 NWCHEM, a very-well parallelized QM code might be better than GAMESS.  THe
 former is also free, assuming you have no export considerations to contend
 with.
 On Wed, Mar 18, 2015 at 6:51 PM, Sergio Manzetti sergio.manzetti*outlook.com
 <owner-chemistry###ccl.net> wrote:
 >
 > Sent to CCL by: "Sergio  Manzetti" [sergio.manzetti__outlook.com]
 > Thanks Brian. At the end of the day, G09 was not able to solve this
 > structure. I am trying GAMESS instead, however I cannot find an equivalent
 > to CASSCF  method in the example section of GAMESS US. Can anyone recommend
 > the most accurate method to treat a very small system (Computational time
 > and speed is irrelevant)?
 >
 > Thanks>
 >
 >