ACES II package from the Quantum Chemistry program at the University of Florida. Is a robust program designed specially for coupled-cluster application. ACES II implements the Coupled Claster and Many Body Perturbation Theory Methods.
ACES II is a series of programs for performing ab inito calculations. The package has a high degree of flexibility, and supports many kinds of calculations at a number of levelS of theory.The major strengths of the program are in performing calculatins using "many-body" correlation. These approaches, broadly categorized as many-body perturbation theory (MBPT) and the coupled-cluster (CC) approximation, offer a reliable treatment of correlation and have the attractive property of size-extensivity, meaning that energies scale properly with the size of the system. As a resultat of this property, MBPT and CC methods are ideally suited for the study of chemical reactions.
ACES II can do analytical gradients for CCSD with RHF, UHF, ROHF, and certain classes of QRHF reference functions. it can also do CCSD gradients for a two-determinant reference for open-shell singlets based on QRHF orbitals. for CCSD(T) it can do analytical gradients for RHF, UHF, and ROHF references. it can also do QCISD and QCISD(T) gradients for RHF and UHF, although we prefer CCSD-based methods to the QCI truncations.