Inclusion of triples correction in the coupled cluster method

The Coupled Cluster theory has proven itself as an effective method for the accurate calculations of correlation energy. A computational program for the full coupled-cluster model (CCSDT) single, double and triple excitation method has been integrated into the Gaussian program. This interface is based on original code that had been developed in late 80's. Single point energy calculations for the HF and OH− molecules verify the accuracy and stability of the newly developed code compared to the old one. Research on the potential energy curve of the $MnO-4$ anion has been conducted. Energy calculations for various Mn-O bond lengths using Hartree-Fock, MP2, MP3, MP4(SDQ), CCSDT), B3LYP, VSXC, PBE and CCSDT method exist. The CCSDT result is in excellent agreement with the experimental value of the Mn-O bond length.