Mod:Hunt Research Group: Using SMD on ILs
This page explains how to use the SMD model to simulate an ionic liquid environment in Gaussian calculations. The SMD model is explained in detail in the original paper here.[1] Its use on ILs is similarly explained here.[2] Many useful solvent parameters are also available in this paper.
Contents
How to simulate a defined solvent environment
Gaussian has many previously defined solvent environments. A list is available at the bottom of this page.[3] For example to use the pre-defined water environment simply insert the following keyword into the method line of your input file. The rest of your method line should specify your functional, basis set, optimisation/other type of calculation as usual.
scrf=(smd,solvent=water)
To use a different solvent to water change the solvent=water part to solvent=something else in the list.
How to simulate a generic solvent environment
The SMD model has many parameters. These are already defined inside Gaussian for the list of defined solvents. If you want to use a solvent not on the list e.g. an ionic liquid, you must define these parameters manually. In this case put the following into the method line:
scrf=(smd,solvent=generic)
Types of SMD model
3 types of SMD for ILs have been defined.[2]
SMD
The standard SMD model. All parameters are determined for the particular IL (or a very similar one) being used as the solvent environment.
SMD-GIL
The generic ionic liquid model. The average values above are used for all parameters, except φ and ψ, which are simply calculated from the chemical formula of the IL.
SMD-PGP
The partial generic parameters model. Any parameter which has been measured for that IL is used. For any parameters which you do not have values for, use the average values.
Solvent parameters and SMD-GIL
The parameters are defined at the bottom of the input file, these parameters are listed in the table below:
| Parameter | Symbol | Name in Gaussian input file | Average value for ILs[2] |
|---|---|---|---|
| Dielectric constant | ε | eps | 11.50 |
| Index of refraction, squared | n2 | epsinf | 2.04 |
| Macroscopic surface tension /cal mol-1 Å-2 | γ | SurfaceTensionAtInterface | 61.24 |
| Abraham hydrogen bond acidity parameter | Σα2H | HBondAcidity | 0.229 |
| Abraham hydrogen bond basicity parameter | Σβ2H | HBondBasicity | 0.265 |
| Fraction of non-hydrogen atoms which are aromatic carbon atoms | φ | CarbonAromaticity | - |
| Fraction of non-hydrogen atoms which are electronegative halogen atoms | ψ | ElectronegativeHalogenicity | - |
Note on parameters
Surface tension
- surface tension is the only parameter with units, those used in SMD are non-standard cal mol-1Å-2
- the SI units are Jm-2 or Nm-1
- typical units are dyn cm-1 where 1 dyn = 1 g cm s-2
- as we tend to work in kJ/mol the energy part of this becomes not J but J/mol
- 1 dyn cm-1 = 0.001N m-1 = 0.001J m-2
- 1 m = 1*1010Å and 1J=0.239cal and 1 mol-1=6.022*1023
- 1 dyn cm-1 = 0.001*0.239cal*6.022*1023mol-1/(1*102*10Å2
- and if you think about this 10*23 on top line cancels with 10*20 on bottom line leaving 10*3 which cancels with the 0.001=10-3 leaving us with 0.239*6.022=1.439
= 1.439 cal/mol</sup>Å2
Example: [C4C1Im][NTf2]
All parameters for this IL have been measured, and can be found in reference 2.[2] That means we can use the standard SMD method.
To get a value for φ take the number of aromatic carbon atoms (3) and divide by the number of non-hydrogen atoms (25). φ = 0.12.
To get a value for ψ take the number of electronegative halogen atoms (6) and divide by the number of non-hydrogen atoms (25). ψ = 0.24.
To define these parameters place the following line at the bottom of the input file (include one blank line before and at least one blank line after):
eps=11.52 epsinf=2.037 SurfaceTensionAtInterface=53.97 HBondAcidity=0.259 HBondBasicity=0.238 CarbonAromaticity=0.12 ElectronegativeHalogenicity=0.24
Kamlet-Taft vs Abraham H-bonding parameters
The SMD model requires Abraham H-bondonding parameters (Σα2H, Σβ2H), however Kamlet-Taft (α, β) measurements are more commonly reported for ILs. To alleviate this problem a relationship between the parameters was investigated, giving the following equations:[2]
Σα2H = 0.4098α + 0.0064
Σβ2H = 0.6138β + 0.0890
Previously the group has developed a simple method for calculating Kamlet-Taft parameters, and the instructions are here.[4]
SMD input database
Here we will keep a database of SMD parameters used by the group. Please add any IL you use, so no-one else has to re-do the research for the parameters! Please follow the template provided so that it is clear where you get each value from.
[C4C1Im][NTf2]
| Name in Gaussian input file | Value | Reference | Comments/calculations |
|---|---|---|---|
| eps | 11.52 | [2] [5] | |
| epsinf | 2.037 | [2] [6] | Value given in reference is n=1.4271, it has been squared to give epsinf=2.037 |
| SurfaceTensionAtInterface | 53.97 | [2] [6] | |
| HBondAcidity | 0.259 | [2] [7] | Kamlet and Taft measurements were reported in ref.[7] Conversion to Abraham values was done using the equations above.[2] |
| HBondBasicity | 0.238 | [2] [7] | |
| CarbonAromaticity | 0.12 | - | There are 25 non-H atoms, 3 are aromatic C atoms. |
| ElectronegativeHalogenicity | 0.24 | - | There are 25 non-H atoms, 6 are electronegative halogen atoms. |
eps=11.52 epsinf=2.037 SurfaceTensionAtInterface=53.97 HBondAcidity=0.259 HBondBasicity=0.238 CarbonAromaticity=0.12 ElectronegativeHalogenicity=0.24
| |||
[C4C1Im][OTf]
| Name in Gaussian input file | Value | Reference | Comments/calculations |
|---|---|---|---|
| eps | 12.9 | [8] | Page 1495, number 11 on the list. |
| epsinf | 2.0665 | [9] | n=1.43755, has been squared to give epsinf=2.0665. Can be found in Table 1, 3rd row. |
| SurfaceTensionAtInterface | |||
| HBondAcidity | 0.263 | [2] [7] | Kamlet and Taft measurements were reported in ref.[7] Conversion to Abraham values was done using the equations above.[2] |
| HBondBasicity | 0.374 | [2] [7] | |
| CarbonAromaticity | 0.167 | - | There are 18 non-H atoms, 3 are aromatic C atoms. |
| ElectronegativeHalogenicity | 0.167 | - | There are 18 non-H atoms, 3 are electronegative halogen atoms. |
eps=12.9 epsinf=2.0665 SurfaceTensionAtInterface= HBondAcidity=0.263 HBondBasicity=0.374 CarbonAromaticity=0.167 ElectronegativeHalogenicity=0.167
| |||
Example table
| Name in Gaussian input file | Value | Reference | Comments/calculations |
|---|---|---|---|
| eps | |||
| epsinf | |||
| SurfaceTensionAtInterface | |||
| HBondAcidity | |||
| HBondBasicity | |||
| CarbonAromaticity | |||
| ElectronegativeHalogenicity | |||
eps= epsinf= SurfaceTensionAtInterface= HBondAcidity= HBondBasicity= CarbonAromaticity= ElectronegativeHalogenicity=
| |||
References
- ↑ Marenich 2009 http://pubs.acs.org/doi/abs/10.1021/jp810292n
- ↑ 2.00 2.01 2.02 2.03 2.04 2.05 2.06 2.07 2.08 2.09 2.10 2.11 2.12 2.13 Bernales 2012 http://pubs.acs.org/doi/abs/10.1021/jp304365v
- ↑ http://www.gaussian.com/g_tech/g_ur/k_scrf.htm
- ↑ http://www.huntresearchgroup.org.uk/research/research_il_alpha_beta_intro.html
- ↑ Daguenet 2006 http://pubs.acs.org/doi/abs/10.1021/jp0604903
- ↑ 6.0 6.1 Huddleston 2001 http://pubs.rsc.org/en/Content/ArticleLanding/2001/GC/b103275p
- ↑ 7.0 7.1 7.2 7.3 7.4 7.5 Crowhurst 2003 http://pubs.rsc.org/en/Content/ArticleLanding/2003/CP/B303095D
- ↑ Huang 2011 http://pubs.acs.org/doi/abs/10.1021/je101184s
- ↑ Gonzalez 2012 http://pubs.acs.org/doi/abs/10.1021/je201334p
