The latter usually defaults to 1.2, but can be specified directly using the option For each center the assumed hybridization is listed together with its formal charge, the final radius, and the solvent-specific scaling parameter Alpha. The following four lines list the results of the UAHF analysis, identifying only three (united atom) centers. The solute cavity is constructed from vdW-spheres represented through regular pentakisdodecahedra, dividing each sphere's surface in 60 elements of equal size. The first four lines repeat settings specific for water or default settings for the PCM model in general. Nord Group Hybr Charge Alpha Radius Bonded to The additional output caused by the PCM solvation model is produced by link 502 responsible for the SCF calculation: -Ĭavity : PENTAKISDODECAHEDRA with 60 initial tesserae Pcm/b3lyp/6-31G(d) sp ethanol in water (Cs)
#Gaussian 09w volume tight free#
The following sample input illustrates the use of the corresponding keywords in the context of a single point calculation (without geometry optimization) on the aqueous solvation free energy of ethanol in its C s symmetric conformation: #P B3LYP/6-31G(d) scf=tight int=finegrid SCRF=(PCM,Read,Solvent=Water) The output generated during PCM calculations can be dramatically extended using the DUMP option. The PCM solvation model is available for calculating energies and gradients at the Hartree-Fock and DFT levels. Additional options can be specified at the end of the input file and read in using the Read modifier of the SCRF keyword. The solvent can be specified using the Solvent= modifier to the SCRF keyword, acceptable solvent names being Water, DMSO, NitroMethane, Methanol, Ethanol, Acetone, DiChloroEthane, DiChloroMethane, TetraHydroFuran, Aniline, ChloroBenzene, Chloroform, Ether, Toluene, Benzene, CarbonTetrachloride, Cyclohexane, Heptane, and Acetonitrile. The implementation of the PCM/UAHF model in Gaussian 98 can be invoked using the SCRF keyword in combination with PCM-specific modifiers. Localization and calculation of the surface charges is approached through systematic division of the spherical surface in small regions (tesserae) of known area and calculation of one point charge per surface element. 1.2 for water) and then adding some more spheres not centered on atoms in order to arrive at a somewhat smoother surface. The electrostatic contribution to the free energy in solution G es uses an approximate version of the solvent excluding surface constructed through scaling all radii by a constant factor (e.g. The latter differs from the former through additional consideration of the (idealized) solvent radius. While calculation of the cavitation energy G cav uses the surface defined by the van der Waals-spheres, the solvent accessible surface is used to calculate the dispersion-repulsion contribution G dr to the solution free energy. In evaluating the three terms in equation (1) this cavity is used in slightly different ways. The vdW-radius of each atom is a function of atom type, connectivity, overall charge of the molecule, and the number of attached hydrogen atoms. In this model the vdW-surface is constructed from spheres located on heavy (that is, non-hydrogen) elements only (United Atom approach). The particular version of PCM that will be discussed here is the one using the United Atom for Hartree-Fock (UAHF) model to build the cavity. The reaction field is represented through point charges located on the surface of the molecular cavity (Apparent Surface Charge (ASC) model). All three terms are calculated using a cavity defined through interlocking van der Waals-spheres centered at atomic positions. These components represent the electrostatic (es) and the dispersion-repulsion (dr) contributions to the free energy, and the cavitation energy (cav).
The PCM model calculates the molecular free energy in solution as the sum over three terms:
The Polarizable Continuum Model (PCM) by Tomasi and coworkers is one of the most frequently used continuum solvation methods and has seen numerous variations over the years.