An efficient closed-shell singles and doubles coupled-cluster method

✍ Scribed by Timothy J. Lee; Julia E. Rice

• Publisher: Elsevier Science
• Year: 1988
• Tongue: English
• Weight: 847 KB
• Volume: 150
• Category: Article
• ISSN: 0009-2614
• DOI: 10.1016/0009-2614(88)80427-5

✦ Synopsis

A reformulated set of equations for the closed-shell singles and doubles couple&luster (CCSD ) method is presented. A computational cost of f&t: +7n$zi + ln# for the n6 steps is obtained, where n, is the number of virtual molecular orbitals included in the CCSD procedure, n, is the number of doubly occupied molecular orbitals and n = n, + n,. Test calculations for the cis and trans isomers of FNNF and planar and pyramidal CH, are presented. Equilibrium structures determined with large Gaussian basis sets at the second-order Moller-Plesset (MP2) perturbation level of theory are reported and used for the other electron correlation methods. With the largest one-particle basis set ( 144 contracted Gaussian functions), the equilibrium geometries of cis-and trans-FNNF agree with experiment. Based on analyses of planar and pyramidal CH, wavefunctions and the calculated inversion barrier, it is suggested that the molecular anion may not exist in a planar configuration but that autodetachment of an electron occurs before the transition state is reached. Comparisons of our new CCSD procedure demonstrate that coupled-cluster methods are not signiBcantly more expensive than similar electron correlation techniques.