46 THE COSMO MODEL

The Conductor-like Screening Model (COSMO) (A. Klamt and G. Schüürmann, J. Chem. Soc. Perkin Trans. II 799-805 (1993)) is currently available for HF (RHF,UHF) and DFT (RKS,UKS) energy calculations and the corresponding gradients.

The COSMO model is invoked by the COSMO card:

COSMO[,option$_1$=value$_1$, option$_2$=value$_2, \ldots$]

where option can be

NPPA

size of the underlying basis grid. The value must satisfy: $value = 10 \times 3^k \times 4^l +2$ (default = 1082; type integer).

NSPA

number of segments for non hydrogen atoms. The value must satisfy: $values = 10 \times 3^k \times 4^l +2$ (default = 92; type integer).

CAVITY

the intersection seams of the molecular surface are closed (1) or open (0) (default = 1; type integer).

EPSILON

dielectric permittivity (default = -1.d0, which means $\epsilon=\infty$; type real)

DISEX

distance criteria for the $\bf A$-matrix setup. Short range interactions (segment centre distances < DISEX $\times$ mean atomic diameter) are calculated using the underlying basis grid. Long range interactions are calculated via the segment centres (default = 10.d0; type float).

ROUTF

factor used for outer cavity construction. The radii of the outer cavity are defined as: $r^{out}_i=r_i+ROUTF \times RSOLV$ (default = 0.85d0; type float)

PHSRAN

phase offset of coordinate randomization (default = 0.d0; type float)

AMPRAN

amplitude factor of coordinate randomization (default = 1.0d-5; type float)

RSOLV

additional radius for cavity construction (default = -1d0, the optimized H radius is used; type float).

MAXNPS

maximal number of surface segments (default = -1, will be estimated; type integer).

It is recommended to change the default values for problematic cases only.

By default the program uses optimized radii if existent and 1.17$\times$vdW radius else. The optimized radii [Å] are: H=1.30, C=2.00, N=1.83, O=1.72, F=1.72, S=2.16, Cl=2.05, Br=2.16, I=2.32. Own proposals can be given directly subsequent to the cosmo card:

RAD,symbol, radius

where the radius has to be given in Å.

Example:
cosmo
rad,O,1.72
rad,H,1.3

Output file:
The COSMO output file will be written after every converged SCF calculation. The segment charges and potentials are corrected by the outlying charge correction. For the total charges and energies corrected and uncorrected values are given. The normal output file contains uncorrected values only. It is recommended to use the corrected values from the output file.

Optimizations:
It is recommended to use optimizer that operates with gradients exclusively. Line search techniques that use energies tends to fail, because of the energy discontinuities which may occur due to a reorganization of the segments after a geometry step. For the same reasons numerical gradients are not recommended.