How to reference EFP
The original implementation of EFP1 (EFP version for water solvent) method in GAMESS:
Paul N. Day, Jan H. Jensen, Mark S. Gordon, Simon P. Webb, Walter J. Stevens, Morris Krauss, David Garmer, Harold Basch, Drora Cohen. An effective fragment method for modeling solvent effects in quantum mechanical calculations. J. Chem. Phys. 1996, 105 (5), 1968–1986.
The original description of the EFP2 (general EFP) model:
Mark S. Gordon, Mark A. Freitag, Pradipta Bandyopadhyay, Jan H. Jensen, Visvaldas Kairys, and Walter J. Stevens. The Effective Fragment Potential Method: A QM-Based MM Approach to Modeling Environmental Effects in Chemistry. J. Phys. Chem. A 2001 105 (2), 293-307
A more recent review of the EFP2 model:
2013 review of EFP2 developments
Mark S. Gordon, Quentin A. Smith, Peng Xu, Lyudmila V. Slipchenko. Accurate First Principles Model Potentials for Intermolecular Interactions. Ann. Rev. Phys. Chem. 2013 64, 553-578.
Excited states QM/EFP models in GAMESS:
2011 review of excited state QM/EFP models and applications
Albert DeFusco, Noriyuki Minezawa, Lyudmila V. Slipchenko, Federico Zahariev, and Mark S. Gordon. Modeling Solvent Effects on Electronic Excited States. J. Phys. Chem. Lett. 2011 2 (17), 2184-2192.
CIS, CIS(D) and EOM-CCSD /EFP models in Q-Chem:
EOM-CCSD and CIS(D) QM/EFP models
Lyudmila V. Slipchenko. Solvation of the Excited States of Chromophores in Polarizable Environment: Orbital Relaxation versus Polarization. J. Phys. Chem. A 2010 114 (33), 8824-8830.
If you use LibEFP library and/or EFP implementation in Q-Chem, please cite:
Ilya A. Kaliman, Lyudmila V. Slipchenko. LIBEFP: A new parallel implementation of the effective fragment potential method as a portable software library. J. Comput. Chem. 2013 34, 2284–2292.
Parallel implementation of LibEFP
Ilya A. Kaliman, Lyudmila V. Slipchenko. Hybrid MPI/OpenMP parallelization of the effective fragment potential method in the libefp software library. J. Comput. Chem. 2015 36, 129–135.