Running Gaussian 03/09, I have had some consistency with CAS(4,4), (6,6) (8,8) but the CAS(10,10) energy deviates from the trend (big increase in energy). I have checked the contributing MOs to the active space and everything is fine. The active space is "inactive" in the course of the calculation. The same calculation with NWChem is unstable but the active space stays active throughout the course of calculation. This inconsistency persist with larger active space (12,12) and (14,14). The complete casscf for my system would be (18,18). Is this a common issue with MCSCF? Thanks for your comments and suggestions
Consistency wrt to the correlation energy. As expected, correlation energy increases with the number of electrons for both Gaussian and NWchem up to CAS(8,8). Beyond the cas(8,8) Gaussian doesn't have fractional occupation where as NWchem's correlation energy doesn't increase with the number of electrons
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