Second-order Rayleigh-Schrödinger Perturbation Theory for the {\sc Grasp}2018 Package: Core-valence Correlations

@misc{gaigalas2026secondorder,
  title = {{Second-order Rayleigh-Schrödinger Perturbation Theory for the \sc Grasp2018 Package: Core-valence Correlations}},
  author = {G. Gaigalas and P. Rynkun and L. Kitovienė},
  howpublished = {arXiv},
  year = {2026},
  month = sep,
  doi = {10.48550/arxiv.2609.15430},
  eprint = {2609.15430},
  archivePrefix = {arXiv},
  url = {https://arxiv.org/abs/2609.15430},
  note = {CC BY-NC-ND 4.0},
}

TY  - UNPB
TI  - Second-order Rayleigh-Schrödinger Perturbation Theory for the {\sc Grasp}2018 Package: Core-valence Correlations
AU  - G. Gaigalas
AU  - P. Rynkun
AU  - L. Kitovienė
PY  - 2026
DA  - 2026/09/14
PB  - arXiv
DO  - 10.48550/arxiv.2609.15430
UR  - https://arxiv.org/abs/2609.15430
AB  - The General Relativistic Atomic Structure package [{\sc Grasp}2018, C. Froese Fischer, G. Gaigalas, P. Jönsson, J. Bieroń, Comput. Phys. Commun. (2019), DOI: 10.1016/j.cpc.2018.10.032], is based on multiconfiguration Dirac-Hartree-Fock and relativistic configuration interaction (RCI) methods for energy structure calculations. Atomic state function used in the program is built from the set of configuration state functions (CSFs). The valence-valence, core-valence and core-core correlations are explicitly included through expansions over CSFs in RCI. We present a combination of RCI and the stationary second-order Rayleigh-Schrödinger many-body perturbation theory in irreducible tensorial form to account for electron core-valence correlations when an atom or ion has any number of valence electrons. This newly developed method, which offers two ways of use, allows a significant reduction of the CSF space for complex atoms and ions. We also demonstrate how the method and program works for energy structure calculation of Cl III element.
ER  -