[Pw_forum] ENVIRON vs COSMO solvation models

[Oliviero Andreussi]

Hi Giuseppe,

You can play with the same two parameters in Environ as well, you just 
need to set env_static_permittivity (and env_optical_permittivity for 
TDDFT) to the ones of the medium you want to simulate. This is assuming 
that you are only interested in the electrostatic interaction with the 
solvent and that the shape of the cavity, i.e. how close to the solute 
you get the continuum solvent, does not depend on the kind of solvent. 
Both these assumptions are implicit in your analogy with COSMO (which by 
the way is a less refined continuum model than the standard PCM or than 
the SCCS model of Environ), but they may be crude depending in the 
system/property you want to study. In particular, I am quite sure that 
standard PCM uses a different scaling of the size of the cavity for 
different solvents.

Clearly, if you are only interested in studying the effects of a 
different dielectric constant of the environment on your embedded 
quantum-mechanical system (e.g. as was done in Fortunelli et al. Angew. 
Chem. Int. Ed. 126, 6787 (2014) doi:10.1002/ange.201403264) you can do 
it very easily with the parameters above. Instead of using one of the 
preset solvent setups (environ_type = 
vacuum/water/water-cation/water-anion), you specify in input only the 
dielectric constant that you want to use, env_static_permittivity = XXX, 
and use the defaults for all the other parameters (which corresponds to 
no contribution from non-electrostatic terms, env_pressure = 0.D0, 
env_surface_tension = 0.D0, and to a shape of the cavity equal to the 
one optimized for water, rhomax = 0.005, rhomin = 0.0001).

Otherwise, if you have to study a well defined solvent and want to be 
more accurate, you would need to redo the parametrization of the model 
for the new solvent, which for Environ only requires to tune 3 (or 4) 
parameters (rhomax and rhomin, which controls the shape of the cavity, 
env_static_permittivity and env_pressure, which are used to model non 
electrostatic effects in a simplified way). Ideally you want to tune 
these parameters to reproduce experimental solvation free energies of a 
reasonable range of solutes in the new solvent (a good database of 
experimental data is from the group of Truhlar 
http://comp.chem.umn.edu/mnsol/ ).

Since I am trying to improve on the documentation of the module, which 
probably is not clear enough, can I ask you which documentation have you 
been studying? The website (www.quantum-environ.org), the input keywords 
(as in the Environ/Doc/ directory or from the website 
http://nebula.wsimg.com/c3d04ee804fb1a1ddb5402d80b7c8194?AccessKeyId=ECF106C2B7F0B5C40F7B&disposition=0&alloworigin=1 
), the references? If you have more doubts on setting up the input or on 
the implemented models, please don't hesitate to write to the forum or 
to contact me directly.

Regards,

Oliviero Andreussi

-- 
Senior Postdoctoral Researcher
École Polytechnique Fédérale de Lausanne (EPFL) and
Università della Svizzera Italiana (USI) of Lugano
USI Campus, Via G. Buffi 17, 6904 Lugano, Switzerland
Emails: oliviero.andreussi @ epfl.ch -or- usi.ch
Tel: +41-(0)58-666-4810 / Skype: olivieroandreussi
Web: https://sites.google.com/site/olivieroandreussi


On 03/08/2016 12:51 PM, Giuseppe Mattioli wrote:
> Dear All
> I was studying the documentation of the ENVIRON 0.2 plugin and it seems that water only is coded as solvent for isolated molecules. I was wondering
> whether there is somewhere a subset of variables (which I was not able to found...) that setup alternative dielectric media as in the case of the
> COSMO model (cited in the ENVIRON documentation), which basically requires the solvent dielectric constant (ground state DFT) or dielectric
> constant+refractive index (TDDFT) only.
> Thank you in advance
> Giuseppe
>
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