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 [1].

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

\[f(\epsilon) = \frac{\epsilon-1}{\epsilon+\chi}\]

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 Yes/No
   Solvent
      Name [...]
   End
End
Solvation
Type:Block
Description:Options for the COSMO (Conductor like Screening Model) solvation model.
Enabled
Type:Bool
Default value:No
GUI name:Include COSMO solvation
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]
GUI name:Solvent
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:

Solvent Name Formula Eps Rad
AceticAcid CH3COOH 6.19 2.83
Acetone CH3COCH3 20.7 3.08
Acetonitrile CH3CN 37.5 2.76
Ammonia NH3 16.9 2.24
Aniline C6H5NH2 6.8 3.31
Benzene C6H6 2.3 3.28
BenzylAlcohol C6H5CH2OH 13.1 3.45
Bromoform CHBr3 4.3 3.26
Butanol C4H9OH 17.5 3.31
isoButanol (CH3)2CHCH2OH 17.9 3.33
tertButanol (CH3)3COH 12.4 3.35
CarbonDisulfide CS2 2.6 2.88
CarbonTetrachloride CCl4 2.2 3.37
Chloroform CHCl3 4.8 3.17
Cyclohexane C6H12 2 3.5
Cyclohexanone C6H10O 15 3.46
Dichlorobenzene C6H4Cl2 9.8 3.54
DiethylEther (CH3CH2)2O 4.34 3.46
Dioxane C4H8O2 2.2 3.24
DMFA (CH3)2NCHO 37 3.13
DMSO (CH3)2SO 46.7 3.04
Ethanol CH3CH2OH 24.55 2.85
EthylAcetate CH3COOCH2CH3 6.02 3.39
Dichloroethane ClCH2CH2Cl 10.66 3.15
EthyleneGlycol HOCH2CH2OH 37.7 2.81
Formamide HCONH2 109.5 2.51
FormicAcid HCOOH 58.5 2.47
Glycerol C3H8O3 42.5 3.07
HexamethylPhosphoramide C6H18N3OP 43.3 4.1
Hexane C6H14 1.88 3.74
Hydrazine N2H4 51.7 2.33
Methanol CH3OH 32.6 2.53
MethylEthylKetone CH3CH2COCH3 18.5 3.3
Dichloromethane CH2Cl2 8.9 2.94
Methylformamide HCONHCH3 182.4 2.86
Methypyrrolidinone C5H9NO 33 3.36
Nitrobenzene C6H5NO2 34.8 3.44
Nitrogen N2 1.45 2.36
Nitromethane CH3NO2 35.87 2.77
PhosphorylChloride POCl3 13.9 3.33
IsoPropanol (CH3)2CHOH 19.9 3.12
Pyridine C5H5N 12.4 3.18
Sulfolane C4H8SO2 43.3 3.35
Tetrahydrofuran C4H8O 7.58 3.18
Toluene C6H5CH3 2.38 3.48
Triethylamine (CH3CH2)3N 2.44 3.81
TrifluoroaceticAcid CF3COOH 8.55 3.12
Water H2O 78.39 1.93

Several other options can be defined in the Solvation block:

Solvation
   CVec [EXACT | FITPOT]
   Charge
      Conv float
      Corr Yes/No
      Iter integer
      Method [CONJ | INVER]
   End
   Enabled Yes/No
   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]
GUI name:Calculate Coulomb interaction
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:Yes
GUI name:Correct for outlying charge
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]
GUI name:Charge determination method
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:No
GUI name:Include COSMO solvation
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]
GUI name:Handle charges
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]
GUI name:Solvent
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]
GUI name:Surface type
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 Yes/No
   NStar integer
End
PeriodicSolvation
Type:Block
Description:Additional options for simulations of periodic structures with solvation.
RemovePointsWithNegativeZ
Type:Bool
Default value:No
GUI name:Only above slab
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.

References

[1]A. Klamt and G. Schüürmann, COSMO: a new approach to dielectric screening in solvents with explicit expressions for the screening energy and its gradient. Journal of the Chemical Society: Perkin Transactions 2, 799 (1993).