The aim of tne project is the development of an integral-direct programme for calculating frequency-dependent polarizabilities and
hyperpolarizabilities for the hierarchy CCS, CC2, CCSD, and CC3 of coupled cluster models. CC2 and CC3 are approximate coupled cluster models, designed with special emphasis on excitation energies and
frequency-dependent properties, recently developed in the group of Poul Joergensen.
It is intended to implement in these programmes the possibility to use atomic orbital basis sets that explicitly depend on the parameters of the electric fields. It is expected, that this approach will improve the convergence of polarizabilities with the basis set dimensions considerably. Combining the integral-direct technique with field-dependent orbitals, these methods can be expected to be applicable to molecules of potential interest for spectroscopical experiments and for the technology of optical devices.
With the hierarchy of coupled cluster models it will be possible to obtain accurate results with an predictable error range.