quantum-espresso/PW/examples/RISM_example

 This example shows how to use the 3-Dimensional Reference Interaction
Site Model (3D-RISM) in pw.x. 3D-RISM calculates the integral equation
of the solvent theory, to provide solvent distributions:

  A.Kovalenko, F.Hirata, Chem. Phys. Lett. 1998, 290, 237-244.

 Solvent molecules have explicit internal structures, and interactions
are defined as classical molecular force fields (written in MOL-format).
The correlation among solvents are decomposed into correlations between
two atoms in solvetns, which are calculated by 1D-RISM. In pw.x, 1D-RISM
is performed at first, and the result allows to calculate 3D-RISM.

 Solute is treated by qunatum mechanical DFT, that is the system with
the ion-cores and the electrons means the solute in pw.x.
3D-RISM calculates distributions around solute for all solvent atoms,
while correlations between solvent atoms are involved.
One can perform 3D-RISM coupled with SCF (i.e. 3D-RISM-SCF).
And pprism.x allows to plot solvent distributions.

  If ESM method is applied for DFT calculation, Laue-RISM is performed
instead of 3D-RISM. The coupling method of ESM and Laue-RISM is called
as ESM-RISM, which is able to simulate solvated slab system. Here,
boundary condition of ESM must be `BC1', and boundary condition of
ESM-RISM becomes Vacuum/Slab/Solvent. ESM-RISM works even if slab is
`charged', because solvent with opposite charge screens slab naturally.

 The details of the example calculation:

1) A H2O molecule in NaCl(aq)
   Performing 3D-RISM-SCF calculation for a H2O molecule, to optimize
   the charge density and the solvent distributions simultaneously.
   The solvent system is aqueous solution of sodium chloride (0.1M).
   Molecular force field for water is Simple Point Charge (SPC) model.
   Also, the atomic positions are relaxed under solvent environment.

2) A HCHO molecule in water
   Performing 3D-RISM-SCF calculation for a HCHO molecule, to optimize
   the charge density and the solvent distributions simultaneously.
   The solvent system is water (SPC). The Lennard-Jones force field
   of HCHO is OPLS-AA. After 3D-RISM-SCF, pprism.x plots distributions
   of the oxygen and the hydrogen atom in solvent water.

3) A Li(100) slab with ethanol
   Performing ESM-RISM calculation for a Li(100) slab with solvent
   ethanol, to optimize the charge density and the solvent distributions
   simultaneously. The system is defined as Vacuum/Li(100)/EtOH, where
   ESM is applied for the Li(100) slab and Laue-RISM is applied for the
   solvent ethanol (OPLS-UA). The Lennard-Jones force field of Li is UFF.
   After ESM-RISM, pprism.x plots distributions of the solvent atoms.

4) A charged Al(111) slab with NaCl(aq)
   Performing ESM-RISM calculation for an Al(111) slab with aqueous
   solution of sodium chloride (5.0M), to optimize the charge density,
   the solvent distributions and the atomic positions of the Al(111)
   simultaneously. The system is defined as Vacuum/Al(111)/NaCl(aq),
   where ESM for the Al(111) and Laue-RISM for NaCl(aq). The Al(111)
   slab has +0.1 charge, which is defined by "tot_charge". If ESM-RISM
   calculation is converged, the Na+ ions will decrease and the Cl- ions
   will increase to cause -0.1 charge for the solvent system.

5) A Cl- ion in NaCl(aq)
   Performing ESM-RISM calculation for an Cl- ion with aqueous solution
   of sodium chloride (1.0M), to obtain the solvation free energy of
   Cl- ion in bulk solution. By defining 'laue_expand_right' and
   'laue_expand_left' in input file, one can calculate the situation
   that an isolated atom/molecule/ion is in bulk solution. Using this
   model one can calculate the salvation free energy with 'explicitly'
   controlled the chemical potential of atoms.