G09

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Gaussian09 vs Gaussian03

Scaling and New Functional Testing

Solvation models, Polarizable Continuum Model (PCM)

As in Gaussian03, the SCRF keyword requests that a calculation be performed in the presence of a solvent by placing the solute in a cavity within the solvent reaction field.

• The integral equation formalism variant IEFPCM, is the default SCRF method. It has not changed from Gaussian03, BUT the formalism used and its implementation has changed. That is: you will get different results in G03 and G09, using the same method.

• The default RADII used in G03 was UAO , whilst now is UFF with spheres placed by default on all Hydrogen atoms. No need to use the SPHEREONH= keyword, except if you use UAO or another radii model that does not have them explicitly.

• It seems to give no "convergence failure" problems, but maybe its too early to say so.

• It is able to perform frequency calculations in solvent, giving enthalpies, free energies, ZPE corrections...

Calculation of solvent effects

Some tests performed on some organic and inorganic species, show that using the default settings (for Gaussian03 defaults + SPHEREONH) the relative energies of a system are on average around 1.5 kcal/mol different between one and the other version of the program. The differences found range between 0.8 and 3.9 kcal/mol.

Some of the species tested are:

                       g09    g03		
([Fe]-H2+) + N(CH3)3        0	  0
([Fe]-H2+) + N(CH3)3     -1.7	-0.6
([Fe]-H-H-N(CH3)3+)      -2.6	 1.3
([Fe]-H) + (+H-N(CH3)3)   5.0	 8.1
----
(BF4-) + N(CH3)3 + (Fe-H2+)	    0      0
(BF4-N(CH3)3-) + (Fe-H2+)         -3.3    -1.9
([Fe]-H2···BF4) + (N(CH3)3)	  -13.3	   -12.1
([Fe]-H2··BF4··N(CH3)3)	  -17.3	   -14.7
([Fe]-H-H-N(CH3)3··BF4)	  -19.7    -16.2
(BF4-···H-N(CH3)3) + (Fe-H2+)    -18.1	   -15.8

energies in kcal/mol.[Fe] is an iron transition metal complex.

According to these results, at least for some systems, the relative energies are significantly different.

Optimization in solvent

• Optimized structures in gas phase of 300-400 basis sets can be re-optimized in solvent in a period of 7 hours- 1 day at cesca (cadi nodes). In some cases the optimization is achieved in few cycles (16), in most cases between 20-40 but and in very few other cases up to 500 cycles are needed.

• Frequency calculations on these structures can be performed in a period of around 3 hours at cadi.

• The relative energies in kcal/mol of some of the single points (SP) and optimized species (OPT) are:

 (in kcal/mol)                    SP      OPT  
(BF4-) + N(CH3)3 + (Fe-H2+)         0       0
(BF4-N(CH3)3-) + (Fe-H2+)         -3.3     -3.7
([Fe]-H2···BF4) + (N(CH3)3)      -13.3	   -15.4
([Fe]-H2··BF4··N(CH3)3)          -17.3	   -19.3
([Fe]-H-H-N(CH3)3··BF4)          -19.7    -21.5
(BF4-···H-N(CH3)3) + (Fe-H2+)    -18.1	   -20.6

Over the tests performed, the difference between the relative energies of the optimized species and the relative energies of the single points are in average: 0.6 kcal/mol.The differences range between +1.1 to -2.5 kcal/mol.

• Optimizations without previous gas phase optimization (from un-optimized species), need aprox. the same number of cycles to optimize it in gas phase or in solvent. For a system with 560 basis sets, 143 cycles, 8 days + 18 hours in cadi are needed for the optimization in solvent and 141 cycles, 7 days and 11 hours also in cadi for the optimization in gas phase.

This is a 17% more time for the optimization in solution.