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# 11.7.2 FDE-Man

(December 20, 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 $molecule section, whereas the first fragment corresponds to the embedded species (A), the second fragment represents the environment (B). Note: The current implementation allows only for closed shell fragments. FDE FDE Turns density embedding on. TYPE: BOOLEAN DEFAULT: False OPTIONS: True Perform an FDET calculation. False Don’t perform FDET calculation. RECOMMENDATION: Set the$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 $rem section. METHOD METHOD Determines which FDET-based method should be used for the embedded wavefunction if FDE = TRUE. TYPE: STRING DEFAULT: None OPTIONS: NAME Use METHOD = NAME, where NAME is either HF for Hartree-Fock theory or else one of the DFT methods listed in Section 5.3.5. RECOMMENDATION: None Other DFT functionals can also be requested with the EXCHANGE and CORRELATION keywords as described in Section 5.4. Note: The current implementation is restricted to mean-field methods that are solved with the SCFMAN module. The standard capabilities to use customized basis sets are also possible with the FDE-Man module. ## 11.7.2.1 FDE-ADC FDE-ADC 923 Prager S. et al. J. Chem. Phys. (2016), 144, pp. 204103. is a density embedding method based on the combination of the Algebraic Diagrammatic Construction scheme for the polarization propagator (ADC, Section 7.11) and Frozen-Density Embedding Theory (FDET). In this particular variant, the subsystem A is represented by a wave function whereas subsystem B is described by a density. The FDE-ADC method uses the linearized FDET approximation. 1265 Zech A., Aquilante F., Wesolowski T. A. J. Chem. Phys. (2015), 143, pp. 164106. Similar to the other methods, the ADC specifications have to be done inside the$rem section, as shown below.

METHOD

METHOD
Determines which FDET-based method should be used if FDE = TRUE.
TYPE:
STRING
DEFAULT:
None
OPTIONS: