| 11:16:45 AM PDT - Fri, Apr 20th 2012 |
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Problem resolution
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Hi Rick,
In order to address this problem I have changed the geometry optimizer a little bit. The problem was that for this system the are some small eigenvalues in the Hessian. On the first point the smallest eigenvalue of the Hessian is 0.4e-3 and along the optimization this declines further to 0.3e-5. Obviously in this context using a Newton-Raphson update of your coordinates is not a good idea as -g/H becomes large due to the developing singularity. So I changed the optimizer to allow me to specify a minimum Hessian eigenvalue, below which the algorithm would switch to using steepest decent for the coordinates corresponding to such eigenvalues. This approach resulted in a much more stable optimization behavior (not exactly fast though). This led to a structure where one of the carbonate oxygens attaches to one of the ethene carbons. At that point it seems that something happens to the electronic structure as the SCF runs into trouble and fails to converge. I have also tried our newly developed second order SCF for DFT calculations but this does not seem to be properly integrated with COSMO yet.
So I think we now know what the issues are. However, at the present time there does not seem to be a way to automatically complete this calculation successfully. If you want I can send you the results of the calculations I have done, just let me know.
Best wishes,
Huub
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