\b[<configuration interaction with singles and doubles> (<CISD>)] uses a linear combination of the reference <Slater determinant> and singly and doubly excited <determinants>. Its many-electron trial state is therefore not restricted to one <determinant>; the orbitals may be held fixed while the configuration coefficients are varied.

Solution

Past exam of the chemistry course of the year 3 of the natural sciences course of the University of Cambridge / 2022 / Paper 2A / Section A / 19 / a / i / Solution

 Solution (source code)