SCM: ADF COSMO-RS 98

Cavity construction

The Esurf type of cavity construction in ADF with default settings does not give a large number of COSMO points. Therefore it is recommended to use the so called Delley type of cavity construction (Ref.[5]), which allows one to construct a surface which has many more points. The Esurf type of cavity construction also allows many more points if one sets the option NFDiv of the subkey DIV of the key SOLVENT to a larger value than the default value of 1. This will not be discussed here further. A figure of a COSMO surface with the Esurf type of cavity construction with default settings is given below. In this figure the small spheres represent the COSMO surface points that are used for the construction of the COSMO surface. The red part represents positive COSMO charge density, the blue part negative COSMO charge density (the coloring scheme is chosen to match the one by Klamt):

Cosmo charge density on the COSMO surface of methanol, Esurf surface (picture made with ADFview)

One can construct a surface which has many more points using a so called Delley surface. For the subkey SURF of the key SOLVENT one can choose delley. The subkey DIV of the key SOLVENT has extra options leb1 (default value 23), leb2 (default value 29), and rleb (default value 1.5 Angstrom). If the cavity radius of an atom is lower than rleb use leb1, otherwise use leb2. These values can be changed: using a higher value for leb1 and leb2 gives more surface points (maximal value leb1, leb2 is 29). A value of 23 means 194 surface points in case of a single atom, and 29 means 302 surface points in case of a single atom Typically one could use leb1 for the surface point of H, and leb2 for the surface points of other elements.

The next figure is made with the following (default for the Delley surface) settings:

SOLVATION
    SURF Delley
    DIV leb1=23 leb2=29 rleb=1.5
    ....
END

Cosmo charge density on the COSMO surface of methanol, Delley surface (picture made with ADFview)

The different ways of constructing the cavity has some consequences for the σ-profile of methanol, see the figure below:

σ-profiles of methanol (picture made with the CRS-GUI)

In this picture the blue line is the σ-profile with the Esurf type of construction, the red line is that with the Delley type of construction with many surface points. For comparison, the green line is the σ-profile of methanol if a large QZ4P basis set is used, again with the Delley type of construction with many surface points.