Abstract
Several coupled-cluster methods based on a single-determinantal reference function have been applied to the model system composed of four hydrogen atoms in a trapezoidal arrangement. For nondegenerate regions all methods with the exception of CCD provide results within 1 mhartree of the exact (FCI) value. For degenerate regions such an accuracy can be achieved with the inclusion of theT3 andT4 clusters, in an iterative and in a noniterative manner. We report results for CCSDT, CCSDTQ-1, CCSD+TQ*(CCSD), CCSD+Q(CCSDT) plus other methods. In particular, the ACP method which has been proposed to indirectly account forT4 terms is critically analyzed by including allT3 contributions.
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Disclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.