Configuration interaction with singles and doubles
= Configuration interaction with singles and doubles
= CISD
{c}
{synonym}
<configuration interaction> retaining a reference <determinant> and its single and double excitations. Conventional matrix-vector iterations have leading $O(o^2v^4)$ work for occupied and virtual dimensions $o,v$, hence $O(N^6)$ when both grow with system size. Truncated <CI> is not generally size extensive.