-level CC2
option; see Section 5.1 for
additional options and parameters of the jobex script that might be
needed or useful for geometry optimizations and
ab initio molecular dynamics calculations.
-level CC2
option;
see Chapter 11 for details about Numforce.
The usage of the Numforce interface for excited states is restricted
to C_{1} symmetry.
Note: using ricc2 in connection with jobex or Numforce requires that the method and the electronic state, for which the gradient should be calculated and written to the interface files, is specified in the option geoopt (see Section 9.3.1) in datagroup $ricc2 (see Section 15.2.13). For calculations on excited states this state has in addition to be included in the input for excitation energies in datagroup $excitations.
RI-SCF reference wavefunctions: The ricc2 can be used in combination with conventional SCF or with the RI-J and RI-JK approximations for SCF, with the exception that the calculation of gradients for a reference wavefunction which employed only the RI-J approximation for the Coulomb matrix but 4-index integrals for the exchange matrix is presently not supported. The implementation gradients in ricc2 assumes that the reference wavefunction has either been calculated with RI approximation (using dscf) or with the RI-JK approximation (using ridft).
See Chapter 6 for a discussion of the
RI approximations in SCF calculations and
15.2.5 for required input.
In geometry optimizations with jobex and for the calculation
of force constants and vibrational spectra with NumForce,
the ricc2 program is used in combination with
the RI-JK approximation for the Hatree-Fock calculation
(using ridft) if jobex and NumForce are invoked with
the -rijk
option.