Size-extensive calculations of static structure factors from the coupled cluster singles and doubles model

The x-ray incoherent scattering factor S(q), which is also called the stati c structure factor, is very sensitive to electron correlation. In this stud y a method for calculating S(q) based on coupled cluster singles and double s (CCSD) approach is developed and the computed S(q) of H2O, CH3OH, CH3CN, C6H6, and C6H12 are compared with experimental results. It is shown that th e CCSD method improves theoretical S(q) of large molecules significantly co mpared with those by configuration interaction singles and doubles (CISD) p reviously employed. (C) 1999 American Institute of Physics. [S0021-9606(99) 30427-X].