The coupled cluster program CC is designed for large-scale correlated calculations of energies and properties using a hierarchy of coupled cluster models: CCS, CC2, CCSD, and CC3, as well as standard methods such as MP2 and CCSD(T). The program offers almost the same options as the other parts of the Dalton program for SCF and MCSCF wave functions. It thus contains a wave function optimization section and a response function section where linear, quadratic and cubic response functions and electronic transition properties are calculated. For CC3 however, it is only possible to calculate the wave function and singlet excitation energies. At the moment, molecular gradients are available up to the CCSD(T) level [] for ground states. London orbitals have so far not been implemented for the calculation of magnetic properties. In the manual, more details can be found about the specific implementations.
An additional feature of the program is that all levels of correlation treatment have been implemented using integral-direct techniques making it possible to run calculations using large basis sets [].
In this chapter the general structure of the input for the
coupled cluster program is described.
The complete input for the coupled cluster program appears as
sections in the input for the SIRIUS PROGRAM, WITH THE GENERAL
INPUT IN THE INPUT SECTION *CC INPUT. IN ORDER TO GET INTO THE CC PROGRAM
ONE HAS TO SPECIFY THE .CC KEYWORD IN THE GENERAL INPUT
SECTION OF SIRIUS
Sec *WAVE FUNCTIONS. FOR INSTANCE, A MINIMAL
INPUT FILE FOR A CCSD(T) ENERGY CALCULATION WOULD BE:
VERBATIM721#
SEVERAL MODELS CAN BE CALCULATED AT THE SAME TIME BY SPECIFYING MORE MODELS IN THE CC INPUT SECTION. THE MODELS SUPPORTED IN THE CC PROGRAM ARE CCS[171], MP2[172], CC2[171], THE CIS(D) EXCITATION ENERGY APPROXIMATION [173], CCSD[174], THE CCSDR(3) EXCITATION ENERGY APPROXIMATION[175], CCSD(T)[176], AND CC3[177,178]. SEVERAL ELECTRONIC PROPERTIES CAN ALSO BE CALCULATED IN ONE CALCULATION BY SPECIFYING SIMULTANEOUSLY THE VARIOUS INPUT SECTIONS IN THE *CC INPUT SECTION AS DETAILED IN THE FOLLOWING SECTIONS.
THERE IS ALSO A POSSIBILITY FOR PERFORMING CAVITY COUPLED CLUSTER
SELF-CONSISTENT-REACTION FIELD CALCULATIONS FOR SOLVENT MODELLING [].