PCM, C-PCM, COSMO, SS(v)PE, polarizable continuum

Polarizable Continuum Solvation Models in Jaguar

The polarizable continuum models (PCM)1 Keyword isolv = 7 in the gen section, or solvent_model = pcm. represent the solvent as a dielectric continuum surrounding a molecule-shaped cavity. The solute's electrostatic potential induces an apparent surface charge on the cavity boundary, which in turn polarizes the solute wave function. This self-consistent reaction field (SCRF) cycle is repeated until convergence.

PCM supports single-point energy calculations, geometry optimizations, transition-state searches, vibrational frequency calculations, and TDDFT excited-state calculations.

To run a PCM solvation calculation, choose PCM from the Solvent model option menu in the Solvation tab, then select a solvent from the Solvent option menu. You can optionally select a PCM variant from the PCM model option menu and a radii set from the PCM radii option menu.

For TDDFT calculations in solution, the solvent optical dielectric constant (the square of the refractive index) is used instead of the static dielectric constant for the response part of the calculation. This value is set automatically for built-in solvents and can be specified manually with the epsout_opt keyword.

A full list of PCM-related keywords and their default values is given in Solvation Keywords in the Jaguar Input File.

Model Variants

Jaguar implements three PCM variants, which differ in how the apparent surface charge is related to the solute electrostatic potential.

• C-PCM (default) — The conductor-like PCM [234].

• COSMO — The conductor-like screening model [232]. Closely related to C-PCM but with a different dielectric charge screening factor. When this variant is selected, Jaguar can write a .cosmo file for use with the COSMOTherm program (set iwrt_cosmo=1). COSMOTherm is not distributed by Schrödinger.

• SS(v)PE — The surface simulation of volume polarization for electrostatics [235], also known as IEF-PCM (integral equation formalism) [236, 237]. This model accounts for charge penetration effects that the conductor-like models neglect.

The C-PCM and COSMO models differ only in the dielectric charge screening factor. See pcm_dcs for details.

Cavity Construction

The PCM cavity surface is constructed from interlocking atomic spheres, each defined by a set of atomic van der Waals radii scaled by a common factor.2 Keywords pcm_radii and pcm_vdwscale in the gen section. The cavity surface is discretized using atom-centered Lebedev grids.

Several sets of atomic radii are available (Bondi, UFF, Klamt, and DRACO), selected with the pcm_radii keyword or the PCM radii option menu. Computed solvation energies are sensitive to the choice of radii and the van der Waals scaling factor (pcm_vdwscale). See pcm_radii for details on each set.

Surface Smoothing

Discretization of the cavity surface can introduce discontinuities in the potential energy surface when atoms move, because grid points may appear or disappear as the atomic spheres shift. These discontinuities can cause convergence problems in geometry optimizations and errors in vibrational frequency calculations. Jaguar applies a smoothing scheme3 Keyword pcm_smooth_method in the gen section. to produce continuous potential energy surfaces. Two smoothing methods are available: the switching/Gaussian approach of Lange and Herbert [238, 239] (the default) and the method of York and Karplus [240].