Bonds schema
============
A full description of the overall Bonds model.

Required Keys
-------------

The following properties are required for the Bonds specification.
   +-------------------------------------------------------------------------------------------------+--------------------------------------------------------------------------------------------------------------------------+----------------------------------------------------------------------------------+
   | Key Name                                                                                        | Description                                                                                                              | Field Type                                                                       |
   +=================================================================================================+==========================================================================================================================+==================================================================================+
   | connectivity                                                                                    | Particle indices  or names e.g. types for each bond and the bond order: (index1, index2, order).                         | array[array]                                                                     |
   +-------------------------------------------------------------------------------------------------+--------------------------------------------------------------------------------------------------------------------------+----------------------------------------------------------------------------------+
   | form                                                                                            | Name or form of the potential. See cls.supported_potentials() for available potentials.                                  | string                                                                           |
   +-------------------------------------------------------------------------------------------------+--------------------------------------------------------------------------------------------------------------------------+----------------------------------------------------------------------------------+
   | lengths                                                                                         | Equilibrium bond lengths. Default unit is Angstroms.                                                                     | array[number]                                                                    |
   +-------------------------------------------------------------------------------------------------+--------------------------------------------------------------------------------------------------------------------------+----------------------------------------------------------------------------------+
   | params                                                                                          | Specific force field parameters model.                                                                                   | object                                                                           |
   +-------------------------------------------------------------------------------------------------+--------------------------------------------------------------------------------------------------------------------------+----------------------------------------------------------------------------------+

Optional Keys
-------------

The following keys are optional for the Bonds specification.
   +-------------------------------------------------------------------------------------------------+--------------------------------------------------------------------------------------------------------------------------+----------------------------------------------------------------------------------+
   | Key Name                                                                                        | Description                                                                                                              | Field Type                                                                       |
   +=================================================================================================+==========================================================================================================================+==================================================================================+
   | lengths_units                                                                                   | Equilibrium bond lengths unit.                                                                                           | string                                                                           |
   +-------------------------------------------------------------------------------------------------+--------------------------------------------------------------------------------------------------------------------------+----------------------------------------------------------------------------------+