Theoretical and Computational Developments
Analytic energy derivatives for coupled-cluster methods describing excited states: General formulas and comparison of computational costs
Article first published online: 21 SEP 2004
Copyright © 1995 John Wiley & Sons, Inc.
International Journal of Quantum Chemistry
Volume 55, Issue 2, pages 151–163, 15 July 1995
How to Cite
Szalay, P. G. (1995), Analytic energy derivatives for coupled-cluster methods describing excited states: General formulas and comparison of computational costs. Int. J. Quantum Chem., 55: 151–163. doi: 10.1002/qua.560550210
- Issue published online: 21 SEP 2004
- Article first published online: 21 SEP 2004
- Manuscript Accepted: 5 OCT 1994
- Manuscript Received: 18 JUL 1994
It is possible to derive energy derivatives for nonvariational (e.g., coupled-cluster) methods invoking the generalized Hellmann–Feynman theorem. In such a procedure, one constructs a functional which, besides the usual wave-function parameters, contains new ones. One set of stationary conditions will reproduce exactly the original equations of the method, while the others will determine the value of the new parameters. We applied this straightforward procedure to derive analytic energy derivatives for several coupled-cluster (CC) methods applicable to excited states such as the Hilbert-space CC method, two-determinetal (TD) CC method, Fock-space CC method, and equation-of-motion–CC (EOM–CC) method. Finally, we compared the computational requirements for the different methods. © 1995 John Wiley & Sons, Inc.