Perspective: Bj?rn roos and direct configuration interaction

摘要

The introduction, impact, and development of the direct configuration interaction (CI) approach are reviewed. The removal of the limitation on the size of CI calculation by eliminating the need to store the Hamiltonian matrix and the streamlining of the calculation of the eigenvector updates in each iteration are seen to be the key transformative contributions of this approach. The initial introduction, limited to closed-shell single-reference CISD (CI with single and double excitations) calculations, underwent successive generalizations, culminating in procedures based on the graphical unitary group approach, allowing applications to multireference CISD calculations for any electronic state.