# solvation

Include effects of solvation through a continuum model. This command can appear in the global context.

### Options

A_matrix_threshold

Cutoff threshold below which the singular values of the COSMO A matrix (i.e. electrostatic interaction between unit surface point charges) are discarded. This is to ensure numerical stability of solving the linear-system equation for obtaining the surface charges.

• The type is real
• The default is 1e-3
• The value must be positive
d_parameter

The d parameter in the Generalized Born method.

The original Generalized Born (GB) method [Still et al., JACS 112, 6127 (1990)] defines the effective solute interatomic distances as $$f_{ij} = \sqrt{r_{ij}^2+\alpha_i\alpha_j\exp[-r_{ij}^2/(d\alpha_i\alpha_j)]}$$ where $$r_{ij}$$ is the physical interatomic distance, $$\alpha_i$$ is the Born radius, and $$d$$ is the value controlled by the dimensionless d_parameter.

While the original model had $$d=4$$, simultaneous optimization of various parameters in the SM6 solvation model [Kelly et al., JCTC 1, 1133 (2005)] led to an improved value of 3.7.

• The type is real
• The default is 3.7
epsilon

Dielectric constant.

• The type is real
• There is no default value.
• The value must be greater than or equal to 1.0
g_shift

Energy shift added to solvated energy to correct energy relative to gas-phase. The shift should be provided in hartree.

• The type is real
• There is no default value.
gb_algorithm

Specify the algorithm for implementing the Generalized Born method.

• The type is string
• The default is surface_integral
• The value must be one of:
incore

Whether to pre-compute the 3-index Coulomb integrals between AO pairs and surface point charges and store them in memory. The requires about (4 * nao^2 * npts) GB of memory where nao is the number of basis functions and npts is the number of surface point charges. This is only recommended for small molecules.

• The type is bool
• The default is true
lebedev

Lebedev order for constructing solvent surface for atoms other than hydrogen.

• The type is int
• The default is 19
lebedev_h

Lebedev order for constructing solvent surface for hydrogen atoms.

• The type is int
• The default is 19
model

Specify the continuum model to use.

• The type is string
• There is no default value.
• The value must be one of:
• cosmo - COSMO solvation model [Klamt and Schüürmann, J Chem Soc Perkin Trans, 2, 799 (1993)].
• gbsa - Generalized-Born solvation model
n_radial_points

Number of radial points for numerical integration for computation of effective Born radii.

• The type is int
• The default is 32
onsager_x

The dimensionless numerical x value in the dielectric screening expression (epsilon - 1) / (epsilon + x). In the original COSMO paper [Klamt and Schüürmann 1993] it is argued that a reasonable default value is x = 0.5, but the COSMO implementation in Gaussian has x = 0.

• The type is real
• The default is 0.5
• The value must be less than or equal to 2.0
parameter_set

Identifier for specific parameterization of the solvation model.

• The type is string
• The default is gfn1_v0
• The value must be one of:
• gfn1_v0 - GBSA solvation model for GFN1-xTB
• gfn1_v1 - GBSA solvation model for GFN1-xTB, including hydrogen-bonding correction for water
• water_gb - GB solvation model for water only -- just for testing
probe_radius

Probe radius for forming the solvent-accessible surface area in GBSA model.

• The type is quantity
• There is no default value.
prune

Threshold for removing surface points with low weights.

• The type is real
• The default is 1e-6
radial_factor

Scale factor for van der Waals or Born radii. The multiplicative factor is applied before the radial_shift (if any).

• The type is real
• There is no default value.
radial_shift

Shift added to the (possibly scaled) van der Waals or Born radii.

• The type is quantity
• There is no default value.
save_surface

Save the surface coordinates and surface charges in four columns in the named file.

• The type is string
• There is no default value.
screening_threshold

Threshold applied to pre-screening point charge integrals based on AO radial overlap integral estimates.

• The type is real
• The default is 1e-11
• The value must be nonnegative
solvent

Specifies solvent for the solvation model.

• The type is string-lowered
• There is no default value.
• The value must be one of:
• water - Water
• benzene - Benzene
• acetonitrile - Acetonitrile
• ether - Diethyl ether
• acetic acid - Acetic acid
surface_area_factor

Surface area factor. In many solvation models (including GBSA and COSMO), non-electrostatic effects (such as Pauli repulsion, cavitation, and dispersion) are modelled by multiplying the solvent-accessible surface area (SASA) by a solvent-dependent factor. While this parameter would normally be internally defined through the specification of a solvent, it can optionally be set by the user using this option.

• The type is real
• There is no default value.
switch

Lengthscale (in bohr) for switching function for interlocking spheres.

• The type is real
• The default is 0.1
switching_length

SASA lengthscale for switching function for interlocking spheres.

• The type is quantity
• The default is 0.3 bohr