11.5.1 Introduction

The Effective Fragment Potential (EFP) method is a computationally inexpensive way of modeling intermolecular interactions in non-covalent systems. The EFP approach can be viewed as a polarizable QM/MM scheme with no empirical parameters. EFP was originally developed by Prof. Mark Gordon’s group ²⁷⁷ Day P. N. et al.
J. Chem. Phys.
(1996), 105, pp. 1968. Link ^{, 423} Gordon M. S. et al.
J. Phys. Chem. A
(2001), 105, pp. 293. Link and implemented in gamess. ¹⁰⁹³ Schmidt M. W. et al.
J. Comput. Chem.
(1983), 14, pp. 1347. Link A review of the EFP theory and applications can be found in Refs.  388 Ghosh D. et al.
J. Phys. Chem. A
(2010), 114, pp. 12739. Link and 422 Gordon M. S. et al.
Chem. Rev.
(2012), 112, pp. 632. Link .

A new implementation of the EFP method based on the libefp library by Dr. Ilya Kaliman (see https://libefp.github.io) has been added to Q-Chem. ⁵⁹⁵ Kaliman I. A., Slipchenko L. V.
J. Comput. Chem.
(2013), 34, pp. 2284. Link ^{, 596} Kaliman I. A., Slipchenko L. V.
J. Comput. Chem.
(2015), 36, pp. 129. Link The new EFP module is called EFPMAN2. EFPMAN2 can run calculations in parallel on shared memory multi-core computers and clusters of computers. EFPMAN2 is interfaced with the CCMAN and CCMAN2 modules to allow coupled cluster and EOM-CC calculations with EFP and with ADCMAN module which allows ADC/EFP calculations. CIS and TDDFT calculations with EFP are also available.