25.2.13 Keywords for reaction-field calculations

For the ricc2 program the reaction-field coupling scheme in COSMO and PE calculations is controled via the data group:

$reaction_field

CCS-like
HF-T1sim
full
PTE
post-SCF
PTED
ptSS
scrf state=(x)
nofast

These options specify the general reaction field coupling scheme , the approximations for the QM densities from which the reaction-field potential and its responses to excitations or perturbations are calculated, and the reference state for state-specific non-equilibrium corrections.

CCS-like

couple the reaction-field to a CCS-like (singles-only) density \[\langle \mathrm{HF} + \bar{T}_1 | \exp(-T_1) a_p^\dagger a_q \exp(T_1)| \mathrm{HF} \rangle\]

HF-T1sim

couple the reaction-field to a mixture of the CCS-like density and a transition density between the HF reference state and a CCS-like (singles-only) approximation to correlated bra state: \[\langle \mathrm{HF} | a_p^\dagger a_q \exp(T_1)| \mathrm{HF} \rangle\] (In Refs. [287, 288] described as sPECC and sPERI-CC2 approximations for the polarizable embedding.)

full

includes for ADC(2) and CC2 first-order doubles contributions to the density, leading to second-order contributions to the reaction-field potential. For CCS equivalent to CCS-like density.

PTED

iterative “Perturbation to the energy and density” reaction-field coupling scheme, requires self-consistent reaction-field (SCRF) cycles around the Hartree-Fock and the correlated calculation until the reaction field is equilibrated with correlated density of a reference state (vide infra). These calculations should be done for COSMO with the script cc2cosmo and for PE with pecc2. By default energies linear response contributions are included for excitation energiess and non-equilibrium contributions for states other the reference state.

post-SCF

non-iterative reaction-field coupling scheme for correlated methods which includes correlation contributions to the ground-state reaction field and linear response contributions to excitation energies and transition moments.

PTE

“Perturbation to the energy” reaction-field coupling scheme for the ground-state energy, includes the frozen-solvent approximation for excitation energies and response properties. These calculations use ground-state Hartree-Fock reaction field throughout without accounting for correlation or response contributions.

nofast

disable linear response contributions (PTED scheme only)

ptSS

enable (state-specific) non-equilibrium contributions for the energies of states different then the reference state (post-SCF scheme only, automatically applied for PTED).

scrf state=(x)

specify reference state for PTED calculations. The syntax for specifying the state is the same as for the option in the data group $exctations (Sec. 25.2.23).