Investigation of a diagnostic for perturbation theory. Comparison to the T1 diagnostic of coupled-cluster theory

✍ Scribed by Timothy J. Lee; Martin Head-Gordon; Alistair P. Rendell

• Publisher: Elsevier Science
• Year: 1995
• Tongue: English
• Weight: 513 KB
• Volume: 243
• Category: Article
• ISSN: 0009-2614
• DOI: 10.1016/0009-2614(95)00875-5

✦ Synopsis

A diagnostic for perturbation theory calculations, 5~2, is defined and numerical results compared to the established .-Y-1 diagnostic from coupled-cluster theory. 5a2 is the lowest-order non-zero contribution to a M~ller-Plesset perturbation expansion of ~-1. 5:2 is a reasonable estimate of the importance of non-dynamical electron correlation, although not as reliable as .7-1. "~2 values ~< 0.012 suggest that low orders of perturbation theory should yield reasonable results; 5a2 values between 0.012 and 0.015 suggest that caution is required in interpreting results from low orders of perturbation theory; S: 2 values >1 0.015 indicate that low orders of perturbation theory are not reliable for accurate results. Although not required mathematically, ~2 is always less than J-1 for the examples studied here.