FDE-ADCPrager:2016 is a density embedding method based on the combination of the Algebraic Diagrammatic Construction scheme for the polarization propagator (ADC, Section 7.10) 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.Zech:2015
The FDE-ADC job control is accomplished in two sections, $rem and $fde. Enabling FDE-ADC, specification of the ADC method and other ADC job control parameters (thresholds, max. iterations etc.) should be set in the $rem section. FDE-ADC also supports the excited state analysis (STATE_ANALYSIS) carried out by the libwfa module.
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) while the second fragment represents the environment (B).
Note: The current implementation allows only for closed shell fragments.
The FDE-ADC job control with respect to embedding parameters is accomplished via options in the $fde input section. The format of the $fde section requires key and value pairs separated by a space character:
$fde <Keyword> <parameter> $end
Note: The following job control variables belong only in the $fde section. Do not place them in the $rem section.
The super-molecular expansion (SE) uses the full basis set of the super-system for calculations on each fragment. Because of the computational cost this option should only be used for small to medium sized super-systems. Note that for visualization of orbitals or densities SE only supports the generation of volumetric data via MAKE_CUBE_FILES (MolDen files are not supported, i.e. MOLDEN_FORMAT should be avoided).
The reassembling of density matrixPrager:2016 (RADM) option allows for calculations on larger systems by only including the basis functions of the embedded species for the ADC calculation. RADM introduces an approximation for the construction of the embedding potential by using an artificially (but cheaply) constructed density matrix for subsystem A. With RADM, all regular options for visualization are supported (MAKE_CUBE_FILES and MOLDEN_FORMAT). The RADM option is the recommended choice for an FDE-ADC calculation.
Analogous to a regular DFT calculation in Q-Chem(by using METHOD) the exchange-correlation functional combination can either be selected with one keyword XC_Func,or by defining X_Func and C_Func (similar to EXCHANGE and CORRELATION).
$rem SYM_IGNORE = true METHOD = adc(2) EE_STATES = 2 BASIS = cc-pvdz FDE = true MEM_STATIC = 1024 MEM_TOTAL = 16000 ADC_DAVIDSON_MAXITER = 100 ADC_DAVIDSON_CONV = 5 $end $molecule 0 1 -- 0 1 C -3.618090 1.376803 -0.020795 O -4.735683 1.525556 0.115023 -- 0 1 O -7.956372 1.485406 0.116792 H -6.992316 1.421133 0.177470 H -8.105846 2.442220 0.111599 $end $fde T_Func TF XC_Func PBE expansion super rhoB_method HF $end
In general the FDE-ADC output indicates all important stages of the FDE-ADC calculation, which are:
Generation of ,
Generation of ,
Construction of the embedding potential,
Start of FDE-ADC calculation and
Final FDE-ADC summary.
In the following table definitions of the terms printed to the output are collected. These quantities are printed for every state, i.e. for every . In addition, the non-electrostatic interactions with respect to the reference density are printed at the top of the FDE-ADC summary.
|Embedded system (A)|
|rho_A <-> rho_B|
|rho_A <-> Nuc_B|
|rho_B <-> Nuc_A|
|Nuc_A <-> Nuc_B|
|integrated v_xc nad|
|integrated v_T nad|
|Final FDE-ADC energies|
|Final Energy (A)|
|Final Energy (A+B)|