Species
=======

Arguments:

  * `nspecies` (int) - Number of species to simulate. 
  * `speciesX` (json object) - Information about speciesX where `X` ranges from 0 to `nspecies-1`. In each `speciesX` object the following must be specified:

    * `label` (string) - String used to label this species throughout the code. This allows more human-readable output and error messages
    * `stat_segment_length` or `b` (float) - Statistical segment length of species (in units of `bref`). Default: 1.
    * `smearing_length` or `a` (float) - Density smearing length. Default: 0. 
    * `smearing_length_units` or `a_units` (string) - Smearing length units. Either `Rg` or `b`. Default: `Rg`.
    * `charge` (float) - Charge of species per statistical segment length. Default: 0. (CONFIRM)

Example (python) ::

  import openfts
  fts = openfts.OpenFTS()
  ... 
  fts.add_species(label='A',stat_segment_length=1.0)
  fts.add_species(label='B',stat_segment_length=1.0)
  ...



Example (json) ::

  "species": {
    "nspecies": 2,
    "species0": {
      "label": "A",
      "stat_segment_length": 1.0
    },
    "species1": {
      "label": "B",
      "stat_segment_length": 1.0
    }
  }