pCI: A parallel configuration interaction software package for high-precision atomic structure calculations

• Published in: Computer physics communications 2025-03, Vol.308, p.109463, Article 109463
• Main Authors: Cheung, Charles, Kozlov, Mikhail G., Porsev, Sergey G., Safronova, Marianna S., Tupitsyn, Ilya I., Bondarev, Andrey I.
• Format: Article
• Language: English
• Subjects: Atomic structure; Configuration interaction; Coupled-cluster; High-performance computing; Isotope shifts; Many-body perturbation theory; Quantum electrodynamics; Radiative transitions
• ISSN: 0010-4655
• DOI: 10.1016/j.cpc.2024.109463

We introduce the pCI software package for high-precision atomic structure calculations. The standard method of calculation is based on the configuration interaction (CI) method to describe valence correlations, but can be extended to attain better accuracy by including core correlations via many-body perturbation theory (CI+MBPT) or the all-order (CI+all-order) method. The software package enables calculations of atomic properties, including energy levels, g-factors, hyperfine structure constants, multipole transition matrix elements, polarizabilities, and isotope shifts. It also features modern high-performance computing paradigms, including dynamic memory allocations and large-scale parallelization via the message-passing interface, to optimize and accelerate computations. To improve accuracy of the calculations, we include a supplementary program package to calculate QED corrections via a variant of QEDMOD, as well as a package to include core correlations. Program Title: pCI CPC Library link to program files:https://doi.org/10.17632/2kn5npnxj7.1 Developer's repository link:https://github.com/ud-pci/pCI Licensing provisions: GPLv3 Programming language: Fortran Supplementary material: Documentation available at https://pci.readthedocs.io Nature of problem: Calculation of atomic and ionic properties, including energy levels, hyperfine structure constants, multipole transition matrix elements, and polarizabilities. Solution method: The software package calculates energies and associated wave functions for the desired atomic states using the configuration interaction method. Using calculated wave functions, different atomic properties can be obtained, including g-factors, hyperfine structure constants, multipole transition amplitudes, polarizabilities, and others. Additional comments including restrictions and unusual features: All serial programs have been compiled and tested with the freely available Intel Fortran compilers “ifx” and “ifort”, and all parallel programs with the OpenMPI wrapper “mpifort” for Intel Fortran compilers. One-electron orbitals outside the nucleus are defined on the radial grid points. Inside the nucleus, they are described in a Taylor expansion over r/R, where R is the nuclear radius. This software package is not designed for calculations of high Rydberg states and continuous spectrum. The parallel programs are intended to be run on large computing clusters. [1]M.G. Kozlov et al., Comput. Phys. Commun. 195 (2015) 199.