11.5.6 Running EFP Jobs

The current version supports single point calculations in systems consisting of ($i$) ab initio and EFP regions (QM/MM); or ($ii$) EFP region only. The ab initio region can be described by conventional quantum methods like HF, DFT, or correlated methods including methods for the excited states [CIS, CIS(D), TDDFT, ADC, EOM-CCSD methods]. Theoretical details on the interface of EFP with EOM-CCSD and CIS(D) can be found in Refs.  1111 Slipchenko L. V.
J. Phys. Chem. A
(2010), 114, pp. 8824. Link and 624 Kosenkov D., Slipchenko L. V.
J. Phys. Chem. A
(2011), 115, pp. 392. Link . ADC/EFP models are described in Ref.  ¹⁰⁷⁹ Sen R., Dreuw A., Faraji S.
Phys. Chem. Chem. Phys.
(2019), 21, pp. 3683. Link .

Note:  EFP provides both implicit (through orbital response) and explicit (as instantaneous response of the polarizable EFP fragments) corrections to the electronic excited states. EFP-modified excitation energies are printed in the property section of the output.

Electrostatic, polarization, exchange-repulsion, and dispersion contributions are calculated between EFs; only electrostatic and polarization terms are evaluated between ab initio and EF regions.

The ab initio region is specified by regular Q-Chem input using $molecule and $rem sections. In calculations with no QM part, the $molecule section should contain a dummy atom (for example, helium).

Positions of EFs are specified in the $efp_fragments section. Two geometry formats, controlled by EFP_COORD_XYZ keyword, are available for fragments, the Euler angle format and the XYZ format. In the Euler angle format, each line in this section contains the information on an individual fragment: fragment’s name and position, specified by center-of-mass coordinates ($x$, $y$, $z$) and the Euler rotation angles ($\alpha$, $\beta$, $\gamma$) relative to the fragment frame, i.e., the coordinates of the standard fragment provided in the fragment library. In the XYZ format, the name of the fragment is provided on the first line followed by three lines specifying names and ($x$, $y$, $z$) coordinates of the first three atoms of the fragment.