Multiconfiguration electron density function for the ATSP2K-package

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.Program summaryProgram title: DENSITYCatalogue identifier: AEFR_v1_0Program summary URL:http://cpc.cs.qub.ac.uk/summaries/AEFR_v1_0.htmlProgram obtainable from: CPC Program Library, Queen's University, Belfast, N. IrelandLicensing provisions: Standard CPC license, http://cpc.cs.qub.ac.uk/licence/licence.htmlNo. of lines in distributed program, including test data, etc.: 6603No. of bytes in distributed program, including test data, etc.: 169 881Distribution format: tar.gzProgramming language: FORTRAN 90Computer: HP XC Cluster Platform 4000Operating system: HP XC System Software 3.2.1, which is a Linux distribution compatible with Red Hat Enterprise Advanced ServerWord size: 32 bitsClassification: 2.1, 2.9, 4.1Subprograms used:Cat IdTitleReferenceADLY_v2_0ATSP2KCPC 176 (2007) 559Full-size tableTable optionsView in workspaceDownload as CSVNature of problem: This program determines the atomic electronic density in the MCHF (LS) or Breit–Pauli (LS J) approximation. It also evaluates the natural orbitals by diagonalizing the density matrix.Solution method: Building the density operator using second quantization – spherical symmetry averaging – evaluating the matrix elements of the one-body excitation operators in the configuration state function (CSF) space using the angular momentum theory in orbital, spin, and quasispin spaces.Restrictions: Original restrictions from ATSP2K package, i.e. all orbitals within a wave function expansion are assumed to be orthonormal. Configuration states are restricted to at most eight subshells in addition to the closed shells common to all configuration states. The maximum size of the working arrays, related to the number of CSFs and active orbitals, is limited by the available memory and disk space.Unusual features: The programming style is essentially F77 with extensions for the POINTER data type and associated memory allocation. These have been available on workstations for more than a decade, but their implementations are compiler dependent. The present code has been installed and tested extensively using the Portland Group, pgf90, compiler.Running time:   The calculation of the electron density for an n=9n=9 complete active space (CAS) MCHF wave function (271 733 CSFs – 45 orbitals) takes around 9 minutes on one AMD Opteron dual-core at 2.4 GHz CPU.References:[1]C. Froese Fischer, G. Tachiev, G. Gaigalas, M.R. Godefroid, An MCHF atomic-structure package for large-scale calculation, Comput. Phys. Commun. 176 (2007) 559–579.