12.5 Effective Fragment Potential Method

12.5.4 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, EOM-CCSD methods]. Theoretical details on the interface of EFP with EOM-CCSD and CIS(D) can be found in Refs. 846 and 488.

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 are available for fragments, Euler angle format and XYZ format. In 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 (α, β, γ) relative to the fragment frame, i.e., the coordinates of the standard fragment provided in the fragment library. The XYZ format is identical to the coordinate format used in gamess; i.e., the name of the fragment is provided on the first line followed by three lines specifying names and x,y,z coordinates of first three atoms of the fragment.

When using EFPMAN2 you can also specify positions and orientations of the fragments using (x, y, z) coordinates of the first three atoms of the fragment. To enable this feature use EFP_COORD_XYZ keyword. The format of input goes as follows: for each fragment the first line should contain the name of the fragment and the following three lines should specify coordinates of the three first atoms belonging to a fragment. The sample input can be found in the examples section below.