COSMO-RS and COSMO-SAC parameters¶

The COSMO-RS model has general parameters and element specific parameters. ADF’s COSMO-SAC 2013-ADF model has general parameters, but also uses some of the COSMO-RS parameters, such as the element specific parameters. There are also technical and accuracy parameters, such as convergence criteria. This section explains how to set these parameters, and shows the default values for these parameters. By default the COSMO-RS method is chosen.

COSMO-RS general parameters¶

CRSPARAMETERS
{RAV         rav}
{APRIME      aprime}
{FCORR       fcorr}
{CHB         chb}
{SIGMAHBOND  sigmahbond}
{AEFF        aeff}
{LAMBDA      lambda}
{OMEGA       omega}
{ETA         eta}
{CHORTF      chortf}
{combi1998 | combi2005}
{hb_all    | hb_hnof}
{hb_temp   | hb_notemp}
{fast      | nofast}
End


The ADF default values are optimized parameters for ADF calculations. The Klamt values can be found in Ref. [1]. See also Ref. [1] for the meaning of the parameters.

Ref. [2] Ref. [2] Ref. [1]
rav ($$r_{av}$$ ) 0.400 0.415 0.5 0.400
aprime (a’) 1510.0 1515.0 1288.0 1550.0
fcorr ($$f_{corr}$$ ) 2.802 2.812 2.4 2.802
chb ($$c_{hb}$$ ) 8850.0 8850.0 7400.0 8400.0
sigmahbond ($$\sigma_{hb}$$ ) 0.00854 0.00849 0.0082 0.00978
aeff ($$a_{eff}$$ ) 6.94 7.62 7.1 5.96
lambda ($$\lambda$$ ) 0.130 0.129 0.14 0.135
omega ($$\omega$$ ) -0.212 -0.217 -0.21 -0.212
eta ($$\eta$$ ) -9.65 -9.91 -9.15 -9.65
chortf ($$c^\perp$$ ) 0.816 0.816 0.816 0.816
combi1998 | combi2005 combi2005 combi1998 combi1998 combi2005
hb_all | hb_hnof hb_hnof hb_hnof hb_hnof hb_hnof
hb_temp | hb_notemp hb_temp hb_notemp hb_notemp hb_temp
fast | nofast fast fast fast fast
chortf
See Ref. [1] for the definitions: $$\sigma_v^\perp = \sigma_v^0 - c^\perp \sigma_v$$
combi1998 | combi2005
If the subkey combi1998 is included a thermodynamically inconsistent combinatorial contribution to the chemical potential $$\mu_i^{comb}$$ of Ref. [1] is used. If the subkey combi2005 is included (default) a thermodynamically consistent combinatorial contribution of Ref. [3] is used. See the section on the combinatorial term and Ref. [3].
hb_all | hb_hnof
If the subkey hb_all is included hydrogen bond interaction can be included between segments that belong to H atoms and all other segments. If the subkey hb_hbnof is included (default) hydrogen bond interaction can be included only between segments that belong to H atoms that are bonded to N, O, or, F, and segments that belong to N, O, or F atoms.
hb_temp | hb_notemp
If the subkey hb_notemp is included the hydrogen bond interaction is not temperature dependent, as in Ref. [1]. If the subkey hb_temp is included (default) the hydrogen bond interaction is temperature dependent, as in Ref. [3]. See the section on the temperature dependent hydrogen bond interaction and Ref. [3].
fast | nofast
If the subkey fast is included the fast approximation is used. This fast approximation is the default. Use nofast for the original approach. See the section on the fast approximation for COSMO-RS calculations.

Links COSMO-RS GUI tutorial: set COSMO-RS parameters [1]

COSMO-RS element specific parameters¶

DISPERSION
{H  dispH}
{C  dispC}
{N  dispN}
{...}
End


The following table gives the element specific dispersion constants. The ADF default values are optimized parameters for ADF calculations. The Klamt values can again be found in Ref. [1]. The constants for F, Si, P, S, Br, and I in the ADF defaults were only fitted to a small number of experimental values or taken from Ref. [3].

Ref. [1]
H -0.0340 -0.0346 -0.041
C -0.0356 -0.0356 -0.037
N -0.0224 -0.0225 -0.027
O -0.0333 -0.0322 -0.042
Cl -0.0485 -0.0487 -0.052
F -0.026
Si -0.04
P -0.045
S -0.052
Br -0.055
I -0.062

Note that not for all elements in the periodic system COSMO-RS parameters were fitted.

Links COSMO-RS GUI tutorial: set COSMO-RS parameters [1]

COSMO-SAC general parameters¶

COSMOSAC2013 | COSMOSAC | COSMOSACDHB
SACPARAMETERS
{AEFF        aeff}
{FDECAY      fdecay}
{SIGMA0      sigma0}
{RN          rn}
{QN          qn}
{AES         aes}
{BES         bes}
{COHOH       cohoh}
{COTOT       cotot}
{COHOT       cohot}
{RAV         rav}
{QS          qs}
{rhbcut      rhbcut}
{hb_temp   | hb_notemp}
End

Ref. [4] Ref. [6] Ref. [8] Ref. [5] Ref. [7]
aeff (aeff ) 6.4813 5.8447 5.8447 7.25 7.25
fdecay (fdecay )   3.57 3.57 3.57 3.57
sigma0 ($$\sigma$$0 ) 0.01233 0.007 0.0063 0.007 0.007
rn (r)   66.69 66.69 66.69 66.69
qn (q) 79.352 79.53 79.53 79.53 79.53
aes (AES ) 7877.13 5920.84 5920.84 6525.69 8451.77
bes (BES ) 0.0 1.3950 108 1.3950 108 1.4859 108 0.0
cohoh (cOH-OH ) 5786.72 3551.10 33306.83 4013.78 3484.42
cotot (cOT-OT ) 2739.58 1077.26 33306.83 932.31 3484.42
cohot (cOH-OT ) 4707.75 3099.31 33306.83 3016.43 3484.42
rav (rav ) 0.51
qs (qs ) 0.57
rhbcut     1.4432
hb_temp | hb_notemp hb_notemp hb_notemp hb_notemp hb_notemp hb_notemp

See also Refs. [4] [5] for the meaning of the parameters aeff , fdecay , $$\sigma$$0 , r, q, AES , BES , cOH-OH , cOT-OT , cOH-OT , rav , qs . The parameter names in [7] have been translated into parameter names used in Ref. [5], by calculating AES from 0.3 fpol aeff 3/2 /(2$$\epsilon_0$$ ), using BES = 0, and using cOH-OH = cOT-OT = cOH-OT = chb . The parameters fdecay and r are not used in COSMO-SAC 2013-ADF [4]. The parameters rav and qs are only used in COSMO-SAC 2013-ADF. The element specific COSMO-SAC 2013-ADF epsilon constants can be set with the block key EPSILON. These element specific epsilon constants can not be used in ADF’s implementation of earlier COSMO-SAC methods. The parameter rhbcut is only used in COSMO-SAC DHB-ADF [8]. Note that the parameters for COSMO-SAC DHB-ADF were reoptimized by Chen et al., and are different than in Ref. [8].

hb_temp | hb_notemp
If the subkey hb_notemp is included (default) the hydrogen bond interaction is not temperature dependent, as in Refs. [7] [5] [4]. If the subkey hb_temp is included the temperature dependence of the hydrogen bond interaction fhb (T) is the same as is described in the section on the temperature dependent hydrogen bond interaction.

Except for COSMO-SAC 2013-ADF, some COSMO-RS specific parameters are used in the next COSMO-SAC methods:

COSMOSAC
SACPARAMETERS
...
{OMEGA       omega}
{ETA         eta}
End

omega ($$\omega$$)   -0.212
eta ($$\eta$$)   -9.00

In ADF2016 these parameters are not used in the COSMO-SAC 2013-ADF method, only in the ADF implementation of the other COSMO-SAC methods. The parameters $$\omega$$, $$\eta$$ and the element specific COSMO-RS dispersion constants are taken from the COSMO-RS model. The element specific COSMO-RS dispersion constants can be set with the block key DISPERSION. $$\omega$$, $$\eta$$, and the element specific COSMO-RS dispersion constants are used in a COSMO-RS like method for the calculation of pure compound vapor pressures.

COSMO-SAC element specific parameters¶

COSMOSAC2013
EPSILON
{H  epsH}
{C  epsC}
{N  epsN}
{...}
End


The following table gives the element specific epsilon constants in case of COSMO-SAC 2013-ADF, see Ref. [4]. Like in the COSMO-RS method, pure compound vapor pressures can be given as input, for example, if experimental values are available. In these values ar not given, in ADF2016 the pure compound vapor pressure will be approximated using the the COSMO-SAC 2013-ADF method, which depend on these element specific epsilon constants. These constants will also have an effect on the calculated activity coefficients in case of a mixture. Note that these only have an effect in the ADF’s COSMO-SAC 2013-ADF implementation.

Ref. [4]
H 338.13
C.sp3 29160.92
C.sp2 30951.83
C.sp 20685.98
N.sp3 23488.54
N.sp2 22663.34
N.sp 6390.40
O.sp3-H 8527.06
O.sp3 8484.38
O.sp2 6736.85
O.sp2-N 12145.28
Cl 8435.13
F 82512.21
P 56067.81
S 45065.19
Br 62947.83
I 105910.88

Note that not for all elements in the periodic system COSMO-SAC 2013-ADF parameters were fitted.

If one leaves the EPSILON block keyword empty the contribution of the mixture dispersion to the activity coefficient will be zero.

EPSILON
End


Technical and accuracy parameters¶

TECHNICAL
{RSCONV rsconv}
{SACCONV sacconv}
{MAXITER maxiter}
{BPCONV bpconv}
{BPMAXITER bpmaxiter}
{SOLCONV solconv}
{SOLMAXITER solmaxiter}
{SOLXILARGE solxilarge}
{EHDELTAT ehdeltaT}
End

symbol Default values
rsconv 10-7 kcal/mol
sacconv 10-7
maxiter 10000
bpconv 10-6 bar
bpmaxiter 40
solconv 10-5 molar fraction
solmaxiter 40
solxilarge 0.99 molar fraction
ehdeltaT 1.0 Kelvin
rsconv
Convergence criterion in kcal/mol in chemical potential calculation, not used in COSMO-SAC 2013-ADF. Default value 1e-7 kcal/mol.
sacconv
Convergence criterion in activity coefficient calculation, only used in COSMO-SAC 2013-ADF. Default value 1e-7.
maxiter
Maximum number of cycles in chemical potential or activity coefficients calculation. Default value 10000.
bpconv
Convergence criterion (bar) for isobar or solvent boiling point calculation. Default value 1e-6 bar.
bpmaxiter
Maximum number of cycles in isobar or solvent boiling point calculation. Default value 40.
solconv
Convergence criterion (molar fraction) used in solubility calculations. Default value 1e-5 molar fraction.
solmaxiter
Maximum number of cycles in solubility calculation. Default value 40.
solxilarge
Threshold for (im-)miscibility (molar fraction) in solubility calculations. Above this value the mixture is considered to be fully miscible. Default value 0.99.
ehdeltaT
$$\Delta T$$ (Kelvin) used in the calculation of the excess enthalpy using the Gibbs-Helmholtz equation and in the calculation of the enthalpy of vaporization using the Clausius-Clapeyron equation using a numerical derivative with respect to T. Default value 1.0 Kelvin.