## Abstract

The configuration interaction (CI) approach to quantum chemical calculations is a well-established means of calculating accurately the solution to the Schrödinger equation for many-electron systems. It represents the many-body electron wavefunction as a sum of spin-projected Slater determinants of orthogonal one-body spin-orbitals. The CI wavefunction becomes the exact solution of the Schrödinger equation as the length of the expansion becomes infinite, however, it is a difficult quantity to visualise and analyse for many-electron problems. We describe a method for efficiently calculating the spin-averaged one- and two-body reduced density matrices ρ _{Ψ}(r̄;r̄^{′}) and Γ _{Ψ}(r̄_{1},r̄_{2};r̄ ^{′}_{1},r̄^{′}_{2}) of an arbitrary CI wavefunction Ψ. These low-dimensional functions are helpful tools for analysing many-body wavefunctions; we illustrate this for the case of the electron-electron cusp. From ρ and Γ one can calculate the matrix elements of any one- or two-body spin-free operator O. For example, if O is an applied electric field, this field can be included into the CI Hamiltonian and polarisation or gating effects may be studied for finite electron systems.

Original language | English |
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Pages (from-to) | 240-249 |

Number of pages | 10 |

Journal | Computational Materials Science |

Volume | 28 |

Issue number | 2 |

DOIs | |

Publication status | Published - Oct 2003 |

Externally published | Yes |

Event | Proceedings of the Symposium on Software Development for Proce - Moscow, Russian Federation Duration: 15 Sep 2002 → 16 Sep 2002 |

## ASJC Scopus subject areas

- Computer Science (all)
- Chemistry (all)
- Materials Science (all)
- Mechanics of Materials
- Physics and Astronomy (all)
- Computational Mathematics