How To Perform a Calculation

Single point calculations:

Call the ricc2 program after a converged SCF calculation.

Geometry optimizations and molecular dynamics:

Invoke jobex with the -level CC2 option; see Section 3.1 for additional options and parameters of the JOBEX script that might be needed or useful for geometry optimizations and ab initio molecular dynamics calculations.

Force constants and vibrational frequencies:

Force constants can be calculated by numerical differentiation on the gradients. Invoke for this NumForce with the -level CC2 option; see Chapter 8 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 interfaces, is specified in the option geoopt (see Section 7.3.1) in datagroup $ricc2 (see Section 12.2.12). For calculations on excited states this state has in addition to be included in the input for excitation energies in datagroup $excitations.