How to cite this article: U. S. Mahapatra, S. Chattopadhyay, J. Comput. Chem. 2012, 33, 1285–1303.
Diagnosis of the performance of the state-specific multireference coupled-cluster method with different truncation schemes†
Article first published online: 15 MAR 2012
Copyright © 2012 Wiley Periodicals, Inc.
Journal of Computational Chemistry
Volume 33, Issue 14, pages 1285–1303, 30 May 2012
How to Cite
Mahapatra, U. S. and Chattopadhyay, S. (2012), Diagnosis of the performance of the state-specific multireference coupled-cluster method with different truncation schemes. J. Comput. Chem., 33: 1285–1303. doi: 10.1002/jcc.22960
- Issue published online: 18 APR 2012
- Article first published online: 15 MAR 2012
- Manuscript Accepted: 7 FEB 2012
- Manuscript Revised: 6 FEB 2012
- Manuscript Received: 13 OCT 2011
- DST. Grant Number: SR/S1/PC-61/2009
- state-specific multireference coupled cluster (SS-MRCC)approach;
- energy surface;
- iterative triples correction;
- optimized geometricalparameters;
- nonparallelism error
We have tested the linked version of a iterative (partial) triples correction for the Jeziorski-Monkhorst ansatz based state-specific multireference coupled cluster (SS-MRCC) approach with singles and doubles (SD) excitations [abbreviated as SS-MRCCSDT-1a and SS-MRCCSDT-1a+d]. The assessments of SS-MRCCSDT-1a and SS-MRCCSDT-1a+d schemes have been performed on the ground potential energy surface (PES) of P4, , and systems which demand the MR description, and on study of the excitation energy between the ground and first excited state for P4 system. Illustrations in the isomerization of cyclobutadiene also show the power of the schemes. One of the designed features of the SS-MRCCSDT-n methods introduced here is that they do not require storage of the triples amplitudes. In the entire range of geometries, we found a definite improvement provided by SS-MRCC with SDT-1a and SDT-1a+d schemes over the standard SD one. In the nondegenerate regions of PES, the closeness of the performance of the single-reference CC to the SS-MRCC methods increases after inclusion of even partial triple excitations. Generally, the performance of the SS-MRCCSDT-1a+d approach is closer to the corresponding full configuration interaction (FCI) one than to the SS-MRCCSDT-1a specially in the degenerate geometries (as is evident from nonparallelism error). The deviation from FCI for the first excited state of the P4 model using various SS-MRCC theories with different truncation schemes obtained by converging on the second root of the effective Hamiltonian has also been reported. We also compare our results with the current generation state-of-the-art single and multireference CC calculations to envisage the usefulness of the present approach. Initial implementation indicates that the SS-MRCCSDT-n formalism can provide not only reliable excitation energies and barrier height even when used in a relatively small model space, but also offers a considerable promise in generating the entire energy surface with low nonparallelity error. © 2012 Wiley Periodicals, Inc.