PCM

[PCM]: Polarizable Continuum Model Options

[PCM] Defaults

Keyword	Default	Description
enabled	False	Enables or disables the PCM reaction-field contribution.
backend	ddx	Selects the PCM backend. The implemented runtime energy path uses ddx.
mode	reference_scf	Selects how the solvent is coupled to the electronic structure calculation.
model	ddpcm	Selects the continuum-solvent model. The recommended/current production value is ddpcm.
solvent	water	Solvent label. Set epsilon explicitly for the desired dielectric constant.
epsilon	78.3553	Static dielectric constant of the solvent.
radii	uff	Cavity-radius keyword. Keep the default unless a development branch documents another radius table.

[PCM] Details

The pcm section enables an implicit-solvent Polarizable Continuum Model (PCM). Instead of placing explicit solvent molecules around the solute, PCM surrounds the molecule with a polarizable dielectric continuum. The solute density polarizes the continuum, and the resulting reaction field is added back into the SCF Fock build.

The first OpenQP PCM implementation is a reference-SCF, single-point energy path. This means:

• Use [input] runtype=energy.
• The active runtime backend is backend=ddx.
• The active continuum model used in the examples is model=ddpcm.
• The supported reference SCF types are RHF and ROHF.
• For MRSF-TDDFT, PCM is applied to the high-spin ROHF reference density before the MRSF response calculation. It is therefore a reference-SCF PCM baseline, not a state-specific excited-state PCM correction.
• PCM analytic gradients, geometry optimizations, Hessians, NACs, and state-specific/non-equilibrium excited-state PCM are not part of this first implementation.

A minimal water ddPCM section is:

[pcm]
enabled=true
backend=ddx
mode=reference_scf
model=ddpcm
solvent=water
epsilon=78.3553
radii=uff

• enabled: Turns the PCM reaction field on or off.

  • Options:
    • False: Run the corresponding gas-phase/vacuum calculation. (Default)
    • True: Add the reference-SCF PCM reaction field to the SCF energy path.
  • Requirements: Current production PCM runs require [input] runtype=energy, [scf] type=rhf or [scf] type=rohf, and an OpenQP build with ddX enabled. If OpenQP is built without ddX support, a PCM-enabled run stops with an error instead of silently returning a vacuum energy.

• backend: Selects the continuum-solvent backend.

  • Default: ddx
  • Use: ddx for the implemented OpenQP/ddX ddPCM energy path.
  • Note: pcmsolver is reserved as an input/backend name, but the first production runtime path is ddX only.

• mode: Selects the solvent-coupling mode.

  • Default: reference_scf
  • Use: reference_scf builds the PCM reaction field from the RHF/ROHF reference SCF density.
  • MRSF note: With [input] method=tdhf and [tdhf] type=mrsf, reference_scf means the solvent is coupled to the high-spin ROHF reference. It does not compute separate state-specific solvent polarization for each response state.

• model: Selects the PCM model.

  • Default: ddpcm
  • Recommended: Use ddpcm with backend=ddx for current examples and production runs.
  • Note: Other model names may be recognized by the input checker for future/development work, but users should keep model=ddpcm unless the relevant runtime branch documents another implemented model.

• solvent: Human-readable solvent label.

  • Default: water
  • Note: The numerical solvent strength is controlled by epsilon. For non-water solvents, set epsilon to the desired static dielectric constant rather than relying only on the label.

• epsilon: Solvent static dielectric constant.

  • Default: 78.3553 for water.
  • Requirements: Must be numeric and greater than 1.
  • Examples: Use epsilon=78.3553 for water. For another solvent, replace this value with the corresponding dielectric constant.

• radii: Cavity-radius keyword.

  • Default: uff
  • Note: Keep the default for standard calculations unless the branch you are using documents another radius-table option.

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