Gaussian 03 Online Manual
This keyword requests that a calculation be performed in the presence of a solvent, using one of the following models:
REQUIRED AND OPTIONAL INPUT: PCM MODELS
Keywords and options specifying details for a PCM calculation (SCRF=PCM, CPCM or IEFPCM) may be specified in an additional blank-line terminated input section provided that the Read option is also specified. Keywords within this section follow general Gaussian input rules. The available keywords are listed in a separate subsection following the examples.
REQUIRED INPUT: ONSAGER MODEL
For the Onsager model (SCRF=Dipole), the solute radius in Angstroms and the dielectric constant of the solvent are read as two free-format real numbers on one line from the input stream. A suitable solute radius is computed by a gas-phase molecular volume calculation (in a separate job step); see the discussion of the Volume keyword.
REQUIRED INPUT: IPCM AND SCI-PCM MODELS
For the IPCM and SCI-PCM models, the input consists of a line specifying the dielectric constant of the solvent and an optional isodensity value (the default for the latter is 0.0004).
OPTION FOR SPECIFYING THE SOLVENT
We list the ε values here for convenience, but be aware it is only one of many internal parameters used to define solvents. Thus, simply changing the ε value will not define a new solvent properly.
METHOD SELECTION OPTIONS
Note that if IEF-PCM is used for an anisotropic or ionic solvent, then items in the PCM input section must be used to select the anisotropic and ionic dielectric models for these types of solvents, using the Read option (see below).
DIPOLE MODEL OPTIONS
PCM MODELS OPTION
IPCM MODEL OPTIONS
SCI-PCM MODEL OPTIONS
The PCM models are available for semi-empirical, HF, DFT, MP2, MP3, MP4(SDQ), QCISD, CCD, CCSD, CASSCF, CIS, TD, CID and CISD energies and HF, DFT, MP2, CIS and CASSCF gradients.
IEFPCM and PCM may be used to compute frequencies for the methods listed for gradients.
Int=AM1 must be used in the route section if SCRF AM1 is specified.
The solvent reaction field for PCM MP2 calculations is equilibrated to the solute electronic density obtained at the SCF level. Note that ΔGsolvation=EPCM-MP2–EMP2 cannot be obtained using the PCM SCFVac option, but must be obtained by comparing the results of two separate calculations, performed in gas-phase and in solvent.
CIS PCM  and TD PCM  calculations are by default non-equilibrium calculations with respect to the polarization process between the solvent reaction field and the charge density of the electronic state indicated in the input (where the ground state is the default). However, equilibrium CIS PCM calculations are the default for geometry optimizations.
By default, CASSCF PCM  calculations corresponds to an equilibrium calculation with respect to the solvent reaction field- solute electronic density polarization process. Calculation of non equilibrium solute-solvent interaction involving two different electronic states (e.g. the initial and final states of a vertical transition) can be performed using the NonEq=type PCM keyword, in two separate job steps (see the PCM input section below).
The IPCM model is available for HF, DFT, MP2, MP3, MP4(SDQ), QCISD, CCD, CCSD, CID, and CISD energies only.
The SCI-PCM model is available for HF and DFT energies and optimizations and numerical frequencies.
The Onsager model is available for HF, DFT, MP2, MP3, MP4(SDQ), QCISD, CCD, CCSD, CID, and CISD energies, and for HF and DFT optimizations and frequency calculations.
The Opt Freq keyword combination may not be used in SCRF=Onsager calculations.
SCRF=PCM and SCRF=IPCM jobs can be restarted from the read-write file by using the Restart keyword in the job's route section. SCRF=SCIPCM calculations which fail during the SCF iterations should be restarted via the SCF=Restart keyword.
PCM Energy. Energy output from the SCRF models other than Onsager appears in the normal way within the output file, followed by additional information about the calculation. For example, here is the section of the output file containing the predicted energy from a PCM calculation:
SCF Done: E(RHF) = -98.569083211 A.U. after 5 cycles Convg = 0.4249D-05 -V/T = 2.0033 S**2 = 0.0000 -------------------------------------------------------------------- Variational PCM results ======================= <psi(f)| H |psi(f)> (a.u.) = -98.568013 <psi(f)|H+V(f)/2|psi(f)> (a.u.) = -98.569083 Total free energy in solution: with all non electrostatic terms (a.u.) = -98.573228 -------------------------------------------------------------------- (Polarized solute)-Solvent (kcal/mol) = -3.27 -------------------------------------------------------------------- Cavitation energy (kcal/mol) = 5.34 Dispersion energy (kcal/mol) = -3.08 Repulsion energy (kcal/mol) = 0.34 Total non electrostatic (kcal/mol) = 2.60 --------------------------------------------------------------------
Additional output lines may appear when various PCM options are included.
The total energy in solution is the sum of the SCF energy and all of the non-electrostatic energy terms (both are highlighted in the output). Note that the PCM results also include the dipole moment in the gas phase and in solution (not shown here), and the various components of the predicted SCRF energy.
For all iterative SCRF methods, note that the energy to use is the one preceding the Convergence achieved message (i.e., the one from the final iteration of the SCRF method).
Onsager Energy. The energy computed by an Onsager SCRF calculation appears in the output file as follows:
Total energy (include solvent energy) = -74.95061789532
Additional Keywords for PCM Calculations
Additional input keywords may be specified for PCM SCRF calculations. They are placed in a separate input section, as in this example:
# HF/6-31++G(d,p) SCF=Tight SCRF=(PCM,Read,Solvent=Cyclohexane) Test PCM SP calculation on hydrogen fluoride 0,1 H F 1 R R=0.9161 TABS=300.0 ALPHA=1.21 TSNUM=70
This Gaussian job performs a PCM energy calculation on the molecule HF using the solvent cyclohexane. The calculation is performed at a temperature of 300 K using a scaling factor for all atoms except acidic hydrogens of 1.21 and a value of 70 tesserae per sphere. The final input section ends as usual with a blank line.
The following keywords are available for controlling PCM calculations (arranged in groups of related items):
SPECIFYING THE SOLVENT
The solvent for the PCM calculation may be specified using the normal Solvent option to the SCRF keyword. The solvent name keyword or ID number may also be placed within the PCM input section. Alternatively, the EPS and RSOLV keywords may be used in the PCM input section to define a solvent explicitly:
Note that if any of these parameters are specified, the others default to the values for water, and so you will probably want to set all of them appropriately.
CALCULATION METHOD VARIATIONS
By default, non-electrostatic energy contributions are computed and printed, but they are not added into the energy and its derivatives during geometry optimizations. The keywords DDis, DRep, and DCav may be used to include them for the rare cases where the non-electrostatic energy terms are known to affect the geometry. Such cases will require care during optimization, and the optimization process may be trickier and more lengthy.
The ICOMP keyword, formerly used to specify the charge compensation mode, is no longer needed and is deprecated.
ANISOTROPIC AND IONIC SOLVENTS
SPECIFYING THE MOLECULAR CAVITY
By default, the program builds up the cavity using the United Atom (UA0) model, i.e. by putting a sphere around each solute heavy atom: hydrogen atoms are enclosed in the sphere of the atom to which they are bonded. There are three UA models available (see below).
The cavity can be extensively modified in the PCM input section: putting spheres around specified hydrogens, changing sphere parameters and the general cavity topology, adding extra spheres to the cavity built by default, and so on. The whole molecular cavity can be also provided by the user in the input section.
UA0: Use the United Atom Topological Model applied on atomic radii of the UFF force field.
UAHF: Use the United Atom Topological Model applied on radii optimized for the HF/6-31G(d) level of theory. These are the recommended radii for for the calculation of ΔGsolvation via the SCFVAC PCM keyword.
UAKS: Use the United Atom Topological Model applied on radii optimized for the PBE0/6-31G(d) level of theory.
UFF: Use radii from the UFF force field. Hydrogens have individual spheres (explicit hydrogens).
PAULING: Use the Pauling (actually Merz-Kollman) atomic radii (explicit hydrogens).
BONDI: Use the Bondi's atomic radii (explicit hydrogens).
When using the UA0 model,
put individual spheres on acidic hydrogens (those bonded to N, O, S, P, Cl and
SES: Solvent Excluding Surface. The surface is generated by the atomic or group spheres and by the spheres created automatically to smooth the surface ("added spheres"). This is the default for electrostatic contribution.
VDW: Van der Waals surface. Uses unscaled atomic radii and skip the generation of "added spheres" to smooth the surface.
SAS: Solvent Accessible Surface. The radius of the solvent is added to the unscaled radii of atoms and/or atomic groups.
ModifySph atom_number radius [alpha]
ExtraSph=N X Y Z radius [alpha] X,Y,Z are the Cartesian coords. in the standard orientation.
atom_number radius [alpha] X Y Z radius [alpha] X,Y,Z are the Cartesian coords. in the standard orientation.
Threshold to discard small tesserae (the default is 10-4
Threshold to discard short edges in a tessera (the default is 5.0*10-7