The following instructions refer to Environ v1.0, for the instructions of previous versions of Environ, please look here.
Environ requires a separate input file, named environ.in, that needs to be present in the running directory. Environ expects to find at least the '&ENVIRON ... /' namelist inside environ.in, which could be empty if using the defaults. This namelist contains the main keywords to activate the different embedding schemes of Environ, plus some global control keywords. By default, all the external contributions are turned off (no continuum dielectric, external pressure, surface tension, pbc corrections, etc.) and the verbosity level is set to minimal.
The SCCS0 set up for the calculation of solvation free energies in water can be simply turned on via the keyword environ_type = 'water', which will activate the continuum dielectric corresponding to the permittivity of liquid water at room temperature and the external pressure and surface tension, which bear no physical meaning and have been tuned in SCCS0 to reproduce the non-electrostatic contributions to the solvation free energy of neutral organic molecules solvated in water.
Each contribution due to the environment can be activated or deactivated independently, by setting the corresponding activation keyword:
Depending on the activated embedding effects, Environ may expect to find other namelists in the environ.in input file. In particular, if an embedding effect that depends on the presence of a smooth interface between the QM and the embedding region (i.e. continuum dielectric, pressure, surface tension, electrolyte) is activated, Environ expects to find the '&BOUNDARY ... /' namelist. In this namelist the details of the construction of the interfaces are specified. By default the Self-Consistent Continuum Solvation interface is selected, thus a smooth interface defined on the electronic density of the system and with parameters optimised to reproduce solvation free energies of small organic molecules in water solutions. Atom-centered soft-sphere interfaces or simplified regular interfaces can also be selected via the available keywords.
Eventually, if an electrostatic embedding effect is activated (i.e. continuum dielectric, external charges, continuum electrolyte or additional electrostatic effects), Environ expects to find the '&ELECTROSTATIC ... /' namelist. In this namelist, the details of the electrostatic calculation are specified. By default a Preconditioned Conjugate Gradient solver for the generalised Poisson equation is adopted (in contrary to the iterative solver implemented as default in Environ-0.X). Accuracy and numerical details of the electrostatic calculation can be specified with the keywords of this namelist.
The full list of available keywords and a brief explanation of their use is reported here and in the documentation directory of the plugin, QE-main-dir/Environ/Doc.