Abstract
The method of sub-iteration, which was previously applied to the higher-order coupled-cluster amplitude equations, is extended to the case of the coupled-cluster Λ equations. The sub-iteration procedure for the Λ equations are found to be highly similar to that for the amplitude equations, and to exhibit a similar improvement in the rate of convergence relative to extrapolation of all or
amplitudes using DIIS. A method of dynamic damping is also presented which is found to effectively recover rapid convergence in the case of oscillatory behaviour in the amplitude or Λ equations. Together, these techniques allow for the convergence of both the amplitude and Λ equations necessary for the calculation of analytic gradients and properties of higher-order coupled-cluster methods without the high memory or disk I/O cost of full DIIS extrapolation.
Acknowledgments
I would like to thank Prof. Jürgen Gauss for inspiring this work, and for his efforts on the CCSDT implementation in CFOUR on which this work is ultimately based. A preliminary version of the original work on sub-iteration in the CC amplitude equations was also presented at the 2015 workshop ‘New Developments in Coupled-Cluster Theory’ co-organised by Prof. Gauss. This work was supported by a start-up grant from Southern Methodist University, and all calculations were performed on the ManeFrame II computing system at SMU.
Disclosure statement
No potential conflict of interest was reported by the author(s).