# Gaussian Tip: Defining Solvents for SMD Calculations

Gaussian offers many pre-defined solvents, which are specified as keywords to the SCRF=Solvent option. In order to specify a solvent not included in this set, it is generally only necessary to specify the value of its dielectric constant ε using additional input to the SCRF keyword, as in this example:

# B3LYP/6-311+G(2d,p) SCRF(Read)

Defining a solvent for IEFPCM

0 1
molecule specification

Eps=28.5            PCM input section
final blank line


For the SMD method, additional parameters are required. These are the 7 items needed to define a solvent for SMD:

 Symbol Definition SCRF= Read Parameter ε Dielectric constant at 298 K. Note that dielectric constant is also called the relative permittivity. Eps n2 The square of the index of refraction at optical frequencies (293 K). This is sometimes called $n_{20}^{D}$. EpsInf α Abraham’s hydrogen bond acidity. In particular, in Abraham’s notation this is called $\sum{\alpha_2^H}$. HbondAcidity β Abraham’s hydrogen bond basicity. In particular in Abraham’s notation this is called $\sum{\beta_2^H}$. HbondBasicity γ γ = γm/γo, where γm is macroscopic surface tension at a liquid-air interface at 298 K, SurfaceTensionAtInterface and γo is 1 cal mol-1Å-2. Conversion factor: 1 dyne/cm = 1.43932 cal mol-1 Å-2 Φ Aromaticity: fraction of non-hydrogenic solvent atoms that are aromatic carbon atoms. CarbonAromaticity Ψ Electronegative halogenicity: fraction of non-hydrogenic solvent atoms that are F, Cl, or Br. ElectronegativeHalogenicity

This example shows the SCRF additional input keywords needed to define the solvent bromobenzene:

 # B3LYP/6-31G(d) 5D SCRF(SMD,Solvent=Generic,Read) 0 1 molecule specification Input section for PCM keywords Eps=5.3954 ε EpsInf=2.432664 n2 HbondAcidity=0.00 α HbondBasicity=0.09 β SurfaceTensionAtInterface=50.72 γ CarbonAromaticity=0.857 φ ElectronegativeHalogenicity=0.143 ψ Blank line terminates PCM input

Last updated on: 26 June 2018.