Foldit is essentially a GUI (graphical user interface) for Rosetta. Rosetta is a suite of software libraries for macromolecular modeling originally developed at the University of Washington in David Baker's Lab. The Rosetta Energy (or Score) is composed of the following terms:

Clashing
  • fa_rep - Lennard-Jones repulsive between atoms in different residues
  • fa_intra_rep - Lennard-Jones repulsive between atoms in the same residue
Packing
  • fa_atr - Lennard-Jones attractive between atoms in different residues
Hiding
Bonding
  • hbond_sr_bb - Backbone-backbone hbonds close in primary sequence
  • hbond_lr_bb - Backbone-backbone hbonds distant in primary sequence
  • hbond_bb_sc - Sidechain-backbone hydrogen bond energy
  • hbond_sc - Sidechain-sidechain hydrogen bond energy
Backbone
  • omega - Omega dihedral in the backbone. A Harmonic constraint on planarity with standard deviation of ~6 deg.
  • p_aa_pp - Probability of amino acid at Φ/Ψ
  • rama - Ramachandran preferences
Sidechain
  • fa_dun - Internal energy of sidechain rotamers as derived from Dunbrack's statistics
Others
  • fa_elec - Coulombic electrostatic potential with a distance-dependent dielectric
  • ref - Reference energy for each amino acid. Balances internal energy of amino acid terms. Plays role in design. 
  • pro_close - Proline ring closure energy and energy of psi angle of preceding residue 
  • dslf_fa13 - Disulfide geometry potential