Solvation¶

COSMO: Conductor like Screening Model and the Solvation-key¶

You can study chemistry in solution, as contrasted to the gas phase, with the implementation in BAND of the Conductor like Screening Model (COSMO) of solvation.[36]

In the COSMO model all solvents are roughly the same, and approximated by an enveloping metal sheet. One explicit dependency on the solvent is that the solvation energy is scaled by

and this depends on the dielectric constant of the solvent, and an empirical factor \(\chi\). The other is that the shape of the surface is influenced by the Rad parameter, see below.

The solvent information is specified in the solvent key of the solvation block. The simplest option is to use one of the pre-defined solvents:

Solvation
   Enabled [True | False]
   Solvent
      Name [...]
   End
End

Solvation

Type:	Block
Description:	Options for the COSMO (Conductor like Screening Model) solvation model.

Enabled

Type:	Bool
Default value:	False
Description:	Use the Conductor like Screening Model (COSMO) to include solvent effects.

Solvent

Type:	Block
Description:	Solvent details

Name

Type:	Multiple Choice
Default value:	Water
Options:	[AceticAcid, Acetone, Acetonitrile, Ammonia, Aniline, Benzene, BenzylAlcohol, Bromoform, Butanol, isoButanol, tertButanol, CarbonDisulfide, CarbonTetrachloride, Chloroform, Cyclohexane, Cyclohexanone, Dichlorobenzene, DiethylEther, Dioxane, DMFA, DMSO, Ethanol, EthylAcetate, Dichloroethane, EthyleneGlycol, Formamide, FormicAcid, Glycerol, HexamethylPhosphoramide, Hexane, Hydrazine, Methanol, MethylEthylKetone, Dichloromethane, Methylformamide, Methypyrrolidinone, Nitrobenzene, Nitrogen, Nitromethane, PhosphorylChloride, IsoPropanol, Pyridine, Sulfolane, Tetrahydrofuran, Toluene, Triethylamine, TrifluoroaceticAcid, Water]
Description:	Name of a pre-defined solvent. A solvent is characterized by the dielectric constant (Eps) and the solvent radius (Rad).

This is the list of possible solvents and their corresponding Eps and Rad values:

Several other options can be defined in the Solvation block:

Solvation
   CVec [EXACT | FITPOT]
   Charge
      Conv float
      Corr [True | False]
      Iter integer
      Method [CONJ | INVER]
   End
   Enabled [True | False]
   Radii # Non-standard block. See details.
      ...
   End
   SCF [VAR | PERT | NONE]
   Solvent
      Del float
      Emp float
      Eps float
      Name [...]
      Rad float
   End
   Surf [Delley | Wsurf | Asurf | Esurf | Klamt]
End

Solvation

Type:	Block
Description:	Options for the COSMO (Conductor like Screening Model) solvation model.

CVec

Type:	Multiple Choice
Default value:	EXACT
Options:	[EXACT, FITPOT]
Description:	Choose how to calculate the Coulomb interaction matrix between the molecule and the point charges on the surface: - EXACT: use exact density, and integrate against the potential of the point charges. This may have inaccuracies when integration points are close to the point charges. - FITPOT: evaluate the molecular potential at the positions of the point charges, and multiply with these charges.

Charge

Type:	Block
Description:	Select the algorithm to determine the charges.

Conv

Type:	Float
Default value:	1e-08
Description:	Charge convergence threshold in iterative COSMO solution.

Corr

Type:	Bool
Default value:	True
Description:	Correct for outlying charge.

Iter

Type:	Integer
Default value:	1000
Description:	Maximum number of iterations to solve COSMO equations.

Method

Type:	Multiple Choice
Default value:	CONJ
Options:	[CONJ, INVER]
Description:	INVER: matrix inversion, CONJ: biconjugate gradient method. The CONJ method is guaranteed to converge with small memory requirements and is normally the preferred method.

Enabled

Type:	Bool
Default value:	False
Description:	Use the Conductor like Screening Model (COSMO) to include solvent effects.

Radii

Type:	Non-standard block
Description:	The values are the radii of the atomic spheres. If not specified the default values are those by Allinge. Format: ‘AtomType value’. e.g.: ‘H 0.7’

SCF

Type:	Multiple Choice
Default value:	VAR
Options:	[VAR, PERT, NONE]
Description:	Determine the point charges either Variational (VAR) or after the SCF as a Perturbation (PERT).

Solvent

Type:	Block
Description:	Solvent details

Del

Type:	Float
Description:	Del is the value of Klamt’s delta_sol parameter, only relevant in case of Klamt surface.

Emp

Type:	Float
Description:	Emp is the empirical scaling factor x for the energy scaling.

Eps

Type:	Float
Description:	User-defined dielectric constant of the solvent (overrides the Eps value of the solvent defined in ‘Name’)

Name

Type:	Multiple Choice
Default value:	Water
Options:	[AceticAcid, Acetone, Acetonitrile, Ammonia, Aniline, Benzene, BenzylAlcohol, Bromoform, Butanol, isoButanol, tertButanol, CarbonDisulfide, CarbonTetrachloride, Chloroform, Cyclohexane, Cyclohexanone, Dichlorobenzene, DiethylEther, Dioxane, DMFA, DMSO, Ethanol, EthylAcetate, Dichloroethane, EthyleneGlycol, Formamide, FormicAcid, Glycerol, HexamethylPhosphoramide, Hexane, Hydrazine, Methanol, MethylEthylKetone, Dichloromethane, Methylformamide, Methypyrrolidinone, Nitrobenzene, Nitrogen, Nitromethane, PhosphorylChloride, IsoPropanol, Pyridine, Sulfolane, Tetrahydrofuran, Toluene, Triethylamine, TrifluoroaceticAcid, Water]
Description:	Name of a pre-defined solvent. A solvent is characterized by the dielectric constant (Eps) and the solvent radius (Rad).

Rad

Type:	Float
Unit:	Angstrom
Description:	User-defined radius of the solvent molecule (overrides the Rad value of the solvent defined in ‘Name’).

Surf

Type:	Multiple Choice
Default value:	Delley
Options:	[Delley, Wsurf, Asurf, Esurf, Klamt]
Description:	Within the COSMO model the molecule is contained in a molecule shaped cavity. Select one of the following surfaces to define the cavity: - Wsurf: Van der Waals surface - Asurf: solvent accessible surface - Esurf: solvent excluding surface - Klamt: Klamt surface - Delley: Delley surface.

Additional keys for periodic systems¶

For the simulation of periodic structures ICW solvation, you may specify the following options:

PeriodicSolvation
   RemovePointsWithNegativeZ [True | False]
   NStar integer
End

PeriodicSolvation

Type:	Block
Description:	Additional options for simulations of periodic structures with solvation.

RemovePointsWithNegativeZ

Type:	Bool
Default value:	False
Description:	Whether the COSMO surface is constructed on both sides of a surface. If one is only interested in the solvation effect on the upper side of a surface (in the Z direction), then this option should be set to ‘True’

NStar

Type:	Integer
Default value:	4
Description:	This option, expecting an integer number (>2), handles the accuracy for the construction of the COMSO surface. The larger the given number the more accurate the construction.

General remarks: The accuracy of the result and the calculation time is influenced by the screening radius SCREENING%RMADEL (see Screening block). If the calculation does take too long, defining a smaller radius does help. But: too small radii, especially smaller than the lattice constants, will give unphysical results.