Open-shell analytical energy gradients for triple excitation many-body, coupled-cluster methods: MBPT(4), CCSD+T(CCSD), CCSD(T),and QCISD(T)

✍ Scribed by John D. Watts; Jürgen Gauss; Rodney J. Bartlett

• Publisher: Elsevier Science
• Year: 1992
• Tongue: English
• Weight: 540 KB
• Volume: 200
• Category: Article
• ISSN: 0009-2614
• DOI: 10.1016/0009-2614(92)87036-o

✦ Synopsis

Equations are derived for the derivatives of the contribution of triple excitations to the energy for the fourth-order many-body perturbation theory (MBPT (4) ), quadratic configuration interaction with singles, doubles, and noniterative triples (QCISD(T ) ), and coupled-cluster with singles, doubles, and noniterative triples (CCSD+T(CCSD) and CCSD(T)) methods. Based on these equations, analytical gradients have been efficiently implemented for the four aforementioned methods for unrestricted Hartree-Fock (UHF) reference functions. This is the first implementation of open-shell analytical gradients for the QCISD(T), CCSD+T( CCSD), and CCSD(T) methods. The new analytical gradient techniques have been used to compute the structure and some properties of the ground state of the HO0 radical with extended basis sets.