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| * [[Solvation models, Polarizable Continuum Model (PCM)]] | | * [[Solvation models, Polarizable Continuum Model (PCM)]] |
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| 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.
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| * 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.
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| * 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.
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| * It seems to give no "convergence failure" problems, but maybe its too early to say so.
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| * It is able to perform frequency calculations in solvent, giving enthalpies, free energies, ZPE corrections...
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| '''Calculation of solvent effects'''
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| 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.
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| Some of the species tested are:
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| ''' g09 g03 '''
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| ([Fe]-H2+) + N(CH3)3 0 0
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| ([Fe]-H2+) + N(CH3)3 -1.7 -0.6
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| ([Fe]-H-H-N(CH3)3+) -2.6 1.3
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| ([Fe]-H) + (+H-N(CH3)3) 5.0 8.1
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| ----
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| (BF4-) + N(CH3)3 + (Fe-H2+) 0 0
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| (BF4-N(CH3)3-) + (Fe-H2+) -3.3 -1.9
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| ([Fe]-H2···BF4) + (N(CH3)3) -13.3 -12.1
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| ([Fe]-H2··BF4··N(CH3)3) -17.3 -14.7
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| ([Fe]-H-H-N(CH3)3··BF4) -19.7 -16.2
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| (BF4-···H-N(CH3)3) + (Fe-H2+) -18.1 -15.8
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| energies in kcal/mol.[Fe] is an iron transition metal complex.
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| According to these results, at least for some systems, the relative energies are significantly different.
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| '''Optimization in solvent'''
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| * 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.
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| * Frequency calculations on these structures can be performed in a period of around 3 hours at cadi.
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| * The relative energies in kcal/mol of some of the single points (SP) and optimized species (OPT) are:
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| (in kcal/mol) '''SP OPT '''
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| (BF4-) + N(CH3)3 + (Fe-H2+) 0 0
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| (BF4-N(CH3)3-) + (Fe-H2+) -3.3 -3.7
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| ([Fe]-H2···BF4) + (N(CH3)3) -13.3 -15.4
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| ([Fe]-H2··BF4··N(CH3)3) -17.3 -19.3
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| ([Fe]-H-H-N(CH3)3··BF4) -19.7 -21.5
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| (BF4-···H-N(CH3)3) + (Fe-H2+) -18.1 -20.6
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| 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.
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| * 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.
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| This is a 17% more time for the optimization in solution.
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