This creates a new energy_data object. The object will have the default parameters. You can, however, specify any of these parameters when you create the object:
edat = energy_data(contact_shell=7.0)
Alternatively, you can set parameters in an existing object:
edat.contact_shell = 7.0
Many commands use energy_data objects. However, for convenience, the environ class also contains an energy_data object, as environ.edat. This is used as the default if you do not give an energy_data parameter, so you can set this to change the objective function used by all functions:
env = environ()
env.edat.contact_shell = 7.0