Multiple substitution effects in configuration interaction calculations

✍ Scribed by Per E.M. Siegbahn

• Publisher: Elsevier Science
• Year: 1978
• Tongue: English
• Weight: 806 KB
• Volume: 55
• Category: Article
• ISSN: 0009-2614
• DOI: 10.1016/0009-2614(78)87046-8

✦ Synopsis

The comrnon way of approximatïng multiple substitntion effects by the nrdinked cluster contrïïuti~n based on the linked cluster theorem is investigated. Fotmally the analysis is done in a confïïation interaction Jauguage without reference to dïagrams. Usïng the hnked cluster theorem a series expansion is then developed for the correction of a CI calculation. including double replacements oniy, for the erratic treatment of unhnked clusters. The fmt term in this series is closely reJa?ed to what is generahy referred to as Davïdson's correction. The next term is proportïonal to the square of the correlation energy and is also very easy to calculate. Finahy numerical examples are given ïllustrating the accuracy of the different approximations. * This model bas been used earlier by for example Abhicbs [25).