SOLVATION Section

Controls implicit solvation. Optional; when absent the calculation runs in vacuo.

Syntax

SOLVATION
  Model           cpcm | cosmo | iefpcm | ssvpe | ddcosmo | ddpcm | smd
  Dielectric      <float>           # static dielectric constant ε
  Solvent         <name>            # named solvent (required for SMD)
  Surface         swig | iswig      # cavity discretization
  Lebedev         <int>             # angular grid points per atom
  VdwScale        <float>           # scaling factor for vdW radii
  ProbeRadius     <float>           # probe radius added to vdW radii (Å)
  MaxCycle        <int>             # solvent response iterations
  Conver          <float>           # solvent response convergence threshold
  Frozen          true | false      # freeze solvent during post-SCF
  Equilibrium     true | false      # equilibrium solvation for TD-DFT
END

Keyword Reference

Electrostatic Models

• ddCOSMO/ddPCM gradient uses adjoint-Lagrangian formulation; the l=0 block is regularized with ε = 1e-3 to stabilize the L-matrix solve.

Model Overview

All seven solvation models belong to one of three engine families. Choose the model that best fits your needs:

• ddCOSMO/ddPCM gradients use the adjoint-Lagrangian formulation. The l=0 block is regularized with ε = 1e-3 to stabilise the L-matrix solve.

• SMD requires a named solvent from the SMD database. A bare Dielectric without Solvent will construct IEF-PCM electrostatics but cannot compute the CDS term, and the calculation will abort.

Per-Model Guides

Each sub-section lists the keywords that actually take effect for that model, how the solvent is resolved, and any model-specific restrictions.

C-PCM (Conductor-like PCM)

The default model. Treats the solvent as a conductor with screening factor f = (ε − 1) / ε.

Supported keywords:

Solvent resolution:

1. If Solvent is given, the dielectric constant is looked up from the built-in solvent table (20 common solvents; see below). If the name is not found, the default 78.3553 is used silently.
2. An explicit Dielectric overrides any solvent lookup.
3. When neither Solvent nor Dielectric is given, the default 78.3553 (water) is used.

Examples:

Using a named solvent:

task: SCF RHF/STO-3G

MOLECULE
  Charge        0
  Multiplicity  1
  Units         Angstrom
END

GEOMETRY
  O   0.000000   0.000000   0.117369
  H   0.756950   0.000000  -0.469476
  H  -0.756950   0.000000  -0.469476
END

SOLVATION
  Model cpcm
  Solvent water
END

Using a custom dielectric without a named solvent:

task: SCF RHF/STO-3G

MOLECULE
  Charge        0
  Multiplicity  1
  Units         Angstrom
END

GEOMETRY
  O   0.000000   0.000000   0.117369
  H   0.756950   0.000000  -0.469476
  H  -0.756950   0.000000  -0.469476
END

SOLVATION
  Model cpcm
  Dielectric 46.826
END

COSMO (Conductor-like Screening Model)

Same keyword set as C-PCM, but uses the COSMO screening factor f = (ε − 1) / (ε + ½).

Supported keywords: Same as C-PCM.

Example:

task: SCF UHF/6-31G(d)

MOLECULE
  Charge        0
  Multiplicity  1
  Units         Angstrom
END

GEOMETRY
  O   0.000000   0.000000   0.117369
  H   0.756950   0.000000  -0.469476
  H  -0.756950   0.000000  -0.469476
END

SOLVATION
  Model cosmo
  Solvent acetonitrile
END

IEF-PCM (Integral Equation Formalism PCM)

Full boundary-element PCM using the S (screened Coulomb) and D (dielectric response) matrices. This is the electrostatic engine used internally when SMD is selected.

Supported keywords: Same as C-PCM.

Example:

task: SCF RHF/6-31+G(d,p)

MOLECULE
  Charge        0
  Multiplicity  1
  Units         Angstrom
END

GEOMETRY
  O   0.000000   0.000000   0.117369
  H   0.756950   0.000000  -0.469476
  H  -0.756950   0.000000  -0.469476
END

SOLVATION
  Model iefpcm
  Solvent tetrahydrofuran
  Surface iswig
END

SS(V)PE (Surface and Simulation of Volume Polarisation for Electrostatics)

Same keyword set as C-PCM, but uses a symmetrised D·A·S formulation to better approximate volume polarisation effects.

Supported keywords: Same as C-PCM.

Example:

SOLVATION
  Model ssvpe
  Solvent dichloromethane
  Lebedev 590
END

ddCOSMO (Domain-Decomposition COSMO)

Uses atom-centred real-spherical-harmonic expansions instead of a cavity surface mesh. This avoids the cost of surface matrix construction but has fewer capabilities.

Supported keywords:

Keywords with no effect (ignored if given, no error):

• Surface — ddCOSMO does not use a surface mesh
• VdwScale — fixed UFF radii × 1.1 are always used
• ProbeRadius — no probe radius is added
• Frozen, Equilibrium — not implemented

Restrictions:

• ❌ No analytical Hessian — calculations requesting freq will fail.
• ❌ ECP not supported — ECP integrals are not available for ddCOSMO.
• ❌ Gradient uses adjoint-Lagrangian — the l=0 block is regularised (ε = 1e-3) to stabilise the L-matrix solve.

Example:

task: SCF RHF/STO-3G

MOLECULE
  Charge        0
  Multiplicity  1
  Units         Angstrom
END

GEOMETRY
  H   0.000000   0.000000   0.000000
  H   0.000000   0.000000   1.400000
END

SOLVATION
  Model ddcosmo
  Solvent water
  Lebedev 302
END

ddPCM (Domain-Decomposition PCM)

Extends ddCOSMO with a dielectric preconditioner (A_diele matrix) for improved accuracy at higher dielectric constants.

Supported keywords and restrictions: Identical to ddCOSMO.

Example:

SOLVATION
  Model ddpcm
  Solvent acetonitrile
  MaxCycle 50
  Conver 1e-8
END

SMD (Solvation Model based on Density)

SMD combines IEF-PCM electrostatics (with SMD-specific cavity radii) with a density-independent CDS (cavity-dispersion-solvent-structure) term. It requires a named solvent from the Minnesota SMD parameter database.

Supported keywords:

Restrictions:

• ⚠️ Solvent is required — the CDS term cannot be computed without a named solvent from the SMD database. A bare Dielectric without Solvent will construct IEF-PCM electrostatics with SMD cavity radii but will not include the CDS term, and the calculation will abort with an error.
• VdwScale and ProbeRadius are parsed but overridden by SMD-specific cavity radii from the database.
• SMD provides its own dielectric constant from the database. Setting Dielectric explicitly overrides the database value (use with care).

Examples:

Using a named solvent from the SMD database:

task: SCF RHF/STO-3G

MOLECULE
  Charge        0
  Multiplicity  1
  Units         Angstrom
END

GEOMETRY
  O   0.000000   0.000000   0.117369
  H   0.756950   0.000000  -0.469476
  H  -0.756950   0.000000  -0.469476
END

SOLVATION
  Model smd
  Solvent water
END

With explicit dielectric override:

task: SCF RHF/STO-3G

MOLECULE
  Charge        0
  Multiplicity  1
  Units         Angstrom
END

GEOMETRY
  O   0.000000   0.000000   0.117369
  H   0.756950   0.000000  -0.469476
  H  -0.756950   0.000000  -0.469476
END

SOLVATION
  Model smd
  Solvent ethanol
  Dielectric 25.0
END

Keyword Quick Matrix

A row for every keyword, with per-model support.

✓ Overridden by SMD cavity radii from the database.

⚠️ Required for SMD; optional for all other models.

Named Solvents

Lookup Table (All Models except SMD)

When Solvent is given without an explicit Dielectric, the dielectric constant is looked up from the built-in table below. Names are matched case-insensitively after stripping spaces, hyphens, underscores, commas, and dots.

For solvents not in this table, use an explicit Dielectric keyword with the desired value.

SMD Solvent Database (SMD Model Only)

SMD requires a solvent name from the Minnesota SMD parameter database. The database contains 179 solvents and is only available when Model = smd.

Quick Reference (Dielectric Constants)

Full Table (All SMD Parameters)

Complete Minnesota SMD descriptors for all supported solvents.