Running Environ

Environ requires a separate input file, named, that needs to be present in the running directory. Environ expects to find a single '&ENVIRON ... /' namelist inside, which could be empty if using the defaults.  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:

  • Continuum dielectric: env_static_permittivity (double-precision real, default=1.D0, activated if >1.D0).
  • External pressure: env_pressure (double-precision real, default=0.D0, activated if !=0.D0).
  • External surface tension: env_surface_tension (double-precision real, default=0.D0, activated if >0.D0).
  • External fixed charge densities: env_external_charge (integer, default= 0, activated if >0).
  • External dielectric regions: env_dielectric_regions (integer, degault=0, activated if >0).

For compatibility with existing implementations in PW, periodic boundary correction schemes are activated through the assume_isolated keyword in the '&SYSTEM ... /' namelist of the standard PW input file. In addition to the values allowed by the standard distribution, none/makov-payne/martyna-tuckerman/esm, Environ allows to specify the point-countercharge correction scheme, both in its version for isolated systems in cubic cells (assume_isolated='pcc') and in its version for two-dimensional systems in orthorombic cells (assume_isolated='slabx/slaby/slabz', where the last letter corresponds to the axis perpendicular to the  plane of the slab). The continuum dielectric contribution is fully compatible with all the assume_isolated options, but for the esm one.

The full list of available keywords and a brief explanation of their use is reported here and in the documentation directory of the plugin, which can be generated with the command 'make doc' inside QE-main-dir/Environ (requires tcl, tcllib, xsltproc, and the PWGui package) and can be found in QE-main-dir/Environ/Doc.