Carlier Group Gaussian User Manual - Virginia Tech

Carlier Group Gaussian User Manual 33
# rb3lyp/6-31g(d) SCRF=(Dipole, Dielectric=7.58, a0=6.63, Solvent=thf)
where SCRF (Self-Consistent Reaction Field) for Onsager calculations is Dipole, the
dielectric constant has to be specified (Gaussian has values for a number of solvents in
their user manual), and the solvent (in this case - THF) is also specified. The average
radius a 0 can be obtained by the method described above.
The energy output looks like the output obtained from an energy calculation in vacuum
and can be obtained using the following command:
egrep SCF filename.out
Onsager optimizations are performed the same way with the addition of opt and freq
options in the route line as follows:
# rb3lyp/6-31g(d) SCRF=(Dipole, Dielectric=7.58, a 0 =6.63, Solvent=thf)
opt freq
Onsager calculations can be performed with DFT and HF methods. However, in
Gaussian 03, they could not be performed using the MP2 method.
Polarized Continuum Model (PCM):
As mentioned earlier, the other solvation model that is frequently used is the
PCM. Unlike in the case of the Onsager model, the PCM comes with the option of
predesigned cavities, owing to which there are no fluctuations associated with the
energies obtained. There are several different flavors of PCM (i.e. CPCM, SCI-PCM);
but in Gaussian03 with our typically large molecules, we have had luck only with PCM
itself.
UA0: This is the default radius in Gaussian03. In this model, the hydrogens are
incorporated in the spherical cavities of the heavy atom they are bonded to.
Bondi: Uses the Bondi atomic radii for all atoms and treats hydrogens explicitly.
Pauling: Uses the Pauling atomic radii for all atoms and treats hydrogens explicitly. Is
recommended for ionic molecules.
Note: The new default for Gaussian 09 is UFF (Universal Force Field), and has explicit
hydrogens unlike UA0. We have not used this yet.
We have used the default settings, as well Bondi and Pauling radii with great success.
In some cases where Bondi has failed in generation of the cavity, Pauling has been
applied successfully.