.. _solvation:

Implicit Solvation
===================


Accurate predictions in quantum chemical calculations require consideration and understanding of the effects of solvents on
chemical systems.
Solvation, the interaction between molecules and solvents, strongly influences their behavior.
In computational chemistry, solvation effects are incorporated through two main approaches: explicit solvation,
in which solvent molecules are explicitly included, and implicit solvation, in which the solvent is treated as a continuum
or dielectric medium surrounding the solute molecule. Implicit solvation models simplify the computational complexity by
treating the solvent as a continuous medium.

This tutorial focuses specifically on implicit solvation in WEASEL, while explicit solvation is covered separately in another
tutorial available :ref:`here<explicitsolv>.

How to sepcify the solvent in WEASEL
-------------------------------------

By default, WEASEL simulations are carried out in implicit water solvent.

Other solvents can be chosen with the following argument:

.. prompt:: bash $

   weasel example.xyz -solvent Octanol

.. _listsolvents:

The available solvents are:

.. list-table::
   :widths: 15 85
   :header-rows: 1
   :class: fixed-width-table

   * - Keyword
     - Solvent option
   * - ``-solvent``
     - | Water, Acetonitrile, Acetone, Ammonia, Benzene, Ethanol, Methanol, CH2Cl2, CCl4,
       | DMF, DMSO, Pyridine, THF, Chloroform, Hexane, Octanol, Cyclohexane, Toluene, *Protein*


.. note::
   It is common practice in biomolecular modeling to model protein structures as cluster models. 
   In such cases, in order to mimic the effect of screening charges in the protein environment, it is common practice to use 
   a dielectric constant of 4. This can be achieved in WEASEL calculations with the solvent option *Protein*.

.. important::

   It can be useful to carry out multiple simulations on a single structure but using different solvents.
   In such a case it can be useful to additionally use the solvent name as label, e.g. 
   
   .. prompt:: bash $

     weasel structure.xyz -solvent acetonitrile -label acetonitrile 

   in order to prevent overwriting the previous results.

Gas phase calculations
----------------------

Also gas phase calculations can be carried out. This is requested with the following argument:

.. prompt:: bash $

   weasel structure.mol2 -gas

Solvents in workflows
---------------------

Different workflows each have their own default solvents (depending on the method, and following the usual standard experimental setups).

The default solvent can be exchanged by another solvent via the command line 
using the `-solvent` keyword:

.. prompt:: bash $

   weasel water.xyz -W UVVis -solvent acetonitrile -label acetonitrile

.. note::
   If your lab setting is different to our defaults you can define new workflows and adapt the workflow-dependent 
   default solvent in the corresponding :ref:`workflow configuration file<workflowsettings>`.


Solvent models
--------------

By default the CPCM implicit solvation model is used. 
Another option is to use the SMD model with the *-smd* keyword:

.. prompt:: bash $

   weasel water.xyz -W UVVis -solvent acetonitrile -smd