Convergence of the coupled-cluster singles, doubles and triples method

✍ Scribed by Gary W. Trucks; Jozef Noga; Rodney J. Bartlett

• Publisher: Elsevier Science
• Year: 1988
• Tongue: English
• Weight: 541 KB
• Volume: 145
• Category: Article
• ISSN: 0009-2614
• DOI: 10.1016/0009-2614(88)87418-9

✦ Synopsis

The convergence of coupled-cluster equations for several cases, CCD, CCSD, CCSDT-n and the full CCSDT is investigated. Comparisons are made between the reduced linear equation (RLE) method for accelerating convergence and simple geometric extrapolation techniques, and between energy and wavefunction convergence criteria.

With the emergence of coupled-cluster theory [ 1,2] among the most accurate quantum-chemical methods for electron correlation, the question of the convergence of the CC equations is important. CCD (coupled-cluster doubles) [ l-4 1, CCSD (singles and doubles) [ 5 1, and various methods for including triples (CCSDT-n) [6-81 and the full CCSDT [9] method have now been developed. Asymptotically, these methods have respectively an N n 6, -n6, -n' and N n8 dependence on the number of basis functions times the number of iterations required to reach convergence. Since it is not iterative, some [ lo] argue that finite-order approximations to CC theory like MBPT, are preferable to converged CC approaches despite the greater accuracy of the latter . In order to combine the considerable advantages of infinite-order CC method without requiring too much time, it is requisite to converge the CC equations rapidly. A thorough study of this problem including some systems intentionally chosen for their poor convergence has already been presented [ 111. That paper proposed a new approach termed the reduced linear equation (RLE) technique to accelerate the convergence of the CC equations, a method we have used successfully for some years [ 12-161. Other investigators have also developed effective