Multiconfiguration electron density function for the ATSP2K-package

TL;DR

This paper introduces a new module in the ATSP2K package for calculating the electron density function of multiconfiguration wave functions, accounting for non-spherical symmetry and utilizing advanced angular momentum techniques.

Contribution

It presents a novel ATSP2K module that computes electron density functions for multiconfiguration wave functions, including non-spherical cases, with a focus on relativistic and non-relativistic approximations.

Findings

Implementation of a new ATSP2K module for electron density calculations.

Method for constructing spherical symmetric density functions from multiconfiguration wave functions.

Use of angular momentum theory and graphical techniques for expectation value calculations.

Abstract

A new ATSP2K module is presented for evaluating the electron density function of any multiconfiguration Hartree-Fock or configuration interaction wave function in the non relativistic or relativistic Breit-Pauli approximation. It is first stressed that the density function is not a priori spherically symmetric in the general open shell case. Ways of building it as a spherical symmetric function are discussed, from which the radial electron density function emerges. This function is written in second quantized coupled tensorial form for exploring the atomic spherical symmetry. The calculation of its expectation value is performed using the angular momentum theory in orbital, spin, and quasispin spaces, adopting a generalized graphical technique. The natural orbitals are evaluated from the diagonalization of the density matrix.