11.7 Frozen-Density Embedding Theory

11.7.1 FDE-Man

(May 16, 2021)

Several FDET-based methods are available in the FDE-Man module of Q-Chem. The FDE-Man job control is accomplished in two sections, $rem and $fde.

The fragments are specified via the fragment descriptors (see Section 12) in the $molecule section, whereas the first fragment corresponds to the embedded species (A), the second fragment represents the environment (B).

Note:  The current implementation allows only for closed shell fragments.

FDE
       Turns density embedding on.
TYPE:
       BOOLEAN
DEFAULT:
       False
OPTIONS:
       True Perform an FDET calculation. False Don’t perform FDET calculation.
RECOMMENDATION:
       Set the $rem variable FDE to TRUE to start a FDET calculation.

Enabling FDE-Man, the specification of the embedding method and other job control parameters (thresholds, max. iterations etc.) should be set in the $rem section.

METHOD
       Determines which FDET-based method should be used for the embedded wavefunction if FDE = TRUE.
TYPE:
       STRING
DEFAULT:
       None
OPTIONS:
       NAME Use METHOD = NAME, where NAME is either HF for Hartree-Fock theory or else one of the DFT methods listed in Section 5.3.4.
RECOMMENDATION:
       None

Other DFT functionals can also be requested with the EXCHANGE and CORRELATION keywords as described in Section 5.4.

Note:  The current implementation is restricted to mean-field methods that are solved with the SCFMAN module.

The standard capabilities to use customized basis sets are also possible with the FDE-Man module.

11.7.1.1 FDE-ADC

FDE-ADC 892 Prager S. et al.
J. Chem. Phys.
(2016), 144, pp. 204103.
Link
is a density embedding method based on the combination of the Algebraic Diagrammatic Construction scheme for the polarization propagator (ADC, Section 7.11) and Frozen-Density Embedding Theory (FDET). In this particular variant, the subsystem A is represented by a wave function whereas subsystem B is described by a density. The FDE-ADC method uses the linearized FDET approximation. 1231 Zech A., Aquilante F., Wesolowski T. A.
J. Chem. Phys.
(2015), 143, pp. 164106.
Link

Similar to the other methods, the ADC specifications have to be done inside the $rem section, as shown below.

METHOD
       Determines which FDET-based method should be used if FDE = TRUE.
TYPE:
       STRING
DEFAULT:
       None
OPTIONS:
       adc(2) Perform an FDE-ADC(2)-s calculation. adc(2)-x Perform an FDE-ADC(2)-x calculation. adc(3) Perform an FDE-ADC(3) calculation (potential constructed with MP(2) density). cvs-adc(2) Perform an FDE-ADC(2)-s calculation of core excitations. cvs-adc(2)-x Perform an FDE-ADC(2)-x calculation of core excitations. cvs-adc(3) Perform an FDE-ADC(3) calculation of core excitations.
RECOMMENDATION:
       None

FDE-ADC also supports the excited state analysis (STATE_ANALYSIS) carried out by the libwfa module.