fix_modify AtC fields <all | none> 
 fix_modify AtC fields <add | delete> <list_of_fields> 
- all | none (keyword) = output all or no fields 
 
- add | delete (keyword) = add or delete the listed output fields 
 
- fields (keyword) = 
 density : mass per unit volume
 displacement : displacement vector
 momentum : momentum per unit volume
 velocity : defined by momentum divided by density
 projected_velocity : simple kernel estimation of atomic velocities
 temperature : temperature derived from the relative atomic kinetic energy (as done by )
 kinetic_temperature : temperature derived from the full kinetic energy
 number_density : simple kernel estimation of number of atoms per unit volume
 stress : Cauchy stress tensor for eulerian analysis (atom_element_map), or 1st Piola-Kirchhoff stress tensor for lagrangian analysis
 transformed_stress : 1st Piola-Kirchhoff stress tensor for eulerian analysis (atom_element_map), or Cauchy stress tensor for lagrangian analysis
 heat_flux : spatial heat flux vector for eulerian, or referential heat flux vector for lagrangian
 potential_energy : potential energy per unit volume
 kinetic_energy : kinetic energy per unit volume
 thermal_energy : thermal energy (kinetic energy - continuum kinetic energy) per unit volume
 internal_energy : total internal energy (potential + thermal) per unit volume
 energy : total energy (potential + kinetic) per unit volume
 number_density : number of atoms per unit volume
 eshelby_stress: configurational stress (energy-momentum) tensor defined by Eshelby [References: Philos. Trans. Royal Soc. London A, Math. Phys. Sci., Vol. 244, No. 877 (1951) pp. 87-112; J. Elasticity, Vol. 5, Nos. 3-4 (1975) pp. 321-335]
 vacancy_concentration: volume fraction of vacancy content
 type_concentration: volume fraction of a specific atom type
 
 fix_modify AtC fields add velocity temperature  
Allows modification of the fields calculated and output by the transfer class. The commands are cumulative, e.g.
  fix_modify AtC fields none  
 followed by 
  fix_modify AtC fields add velocity temperature  
 will only output the velocity and temperature fields. 
Must be used with the hardy/field type of AtC fix, see fix atc command. Currently, the stress and heat flux formulas are only correct for central force potentials, e.g. Lennard-Jones and EAM but not Stillinger-Weber. 
See fix_modify AtC gradients , fix_modify AtC rates and fix_modify AtC computes 
By default, no fields are output