Second-Order Rayleigh-Schrödinger Perturbation Theory for the GRASP2018 Package: Core Correlations

@misc{gaigalas2026secondorder,
  title = {{Second-Order Rayleigh-Schrödinger Perturbation Theory for the GRASP2018 Package: Core Correlations}},
  author = {G. Gaigalas and P. Rynkun and L. Kitovienė},
  howpublished = {arXiv},
  year = {2026},
  month = sep,
  doi = {10.48550/arxiv.2609.16761},
  eprint = {2609.16761},
  archivePrefix = {arXiv},
  url = {https://arxiv.org/abs/2609.16761},
  note = {CC BY-NC-ND 4.0},
}

TY  - UNPB
TI  - Second-Order Rayleigh-Schrödinger Perturbation Theory for the GRASP2018 Package: Core Correlations
AU  - G. Gaigalas
AU  - P. Rynkun
AU  - L. Kitovienė
PY  - 2026
DA  - 2026/09/15
PB  - arXiv
DO  - 10.48550/arxiv.2609.16761
UR  - https://arxiv.org/abs/2609.16761
AB  - The paper presents a further development of the method G. Gaigalas, P. Rynkun, L. Kitovienė, Second-Order of Rayleigh-Schrödinger Perturbation Theory for the {\sc Grasp}2018 Package: Core-Valence Correlations, {\em Lithuanian Journal of Physics}, 64, No. 1, 20-39 (2024) (https://doi.org/10.3952/physics.2024.64.1.3), based on a combination of the relativistic configuration interaction method and on the stationary second-order Rayleigh-Schrödinger many-body perturbation theory in an irreducible tensorial form. In this extension the perturbation theory accounts for both electron core-valence and core correlations when an atom or ion has any number of valence electrons meanwhile relativistic configuration interaction accounts for the rest of correlations. This allows a significant reduction of the space of the configuration state function for complex atoms and ions. We also demonstrate how this method works for energy structure calculation of Fe XV ion.
ER  -