Configuration Interaction Method Research Articles

Quantum Proton Effects from Density Matrix Renormalization Group Calculations.

We recently introduced [J. Chem. Phys. 2020, 152, 204103] the nuclear-electronic all-particle density matrix renormalization group (NEAP-DMRG) method to solve the molecular Schrödinger equation, based on a stochastically optimized orbital basis, without invoking the Born-Oppenheimer approximation. In this work, we combine the DMRG method with the nuclear-electronic Hartree-Fock (NEHF-DMRG) approach, treating nuclei and electrons on the same footing. Inter- and intraspecies correlations are described within the DMRG method without truncating the excitation degree of the full configuration interaction wave function. We extend the concept of orbital entanglement and mutual information to nuclear-electronic wave functions and demonstrate that they are reliable metrics to detect strong correlation effects. We apply the NEHF-DMRG method to the HeHHe+ molecular ion, to obtain accurate proton densities, ground-state total energies, and vibrational transition frequencies by comparison with state-of-the-art data obtained with grid-based approaches and modern configuration interaction methods. For HCN, we improve on the accuracy of the latter approaches with respect to both the ground-state absolute energy and proton density, which is a major challenge for multireference nuclear-electronic state-of-the-art methods.

Molecular opacities of <inline-formula><tex-math id="Z-20221003130318">\begin{document}$ {{\text{X}}^{2}}{\Sigma}_{\text{g}}^{+} $\end{document}</tex-math><alternatives><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="19-20220734_Z-20221003130318.jpg"/><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="19-20220734_Z-20221003130318.png"/></alternatives></inline-formula>, A<sup>2</sup>Π<sub>u</sub> and <inline-formula><tex-math id="Z-20221003130305">\begin{document}$ {{\text{B}}^{2}}{\Sigma}_{\text{u}}^{+} $\end{document}</tex-math><alternatives><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="19-20220734_Z-20221003130305.jpg"/><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="19-20220734_Z-20221003130305.png"/></alternatives></inline-formula> states of nitrogen cation

The potential curves, spectroscopic constants and dipole moments for <inline-formula><tex-math id="Z-20221003130344">\begin{document}$ {{\text{X}}^{2}}{\Sigma}_{\text{g}}^{+} $\end{document}</tex-math><alternatives><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="19-20220734_Z-20221003130344.jpg"/><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="19-20220734_Z-20221003130344.png"/></alternatives></inline-formula>, A<sup>2</sup>Π<sub>u</sub> and <inline-formula><tex-math id="Z-20221003130359">\begin{document}$ {{\text{B}}^{2}}{\Sigma}_{\text{u}}^{+} $\end{document}</tex-math><alternatives><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="19-20220734_Z-20221003130359.jpg"/><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="19-20220734_Z-20221003130359.png"/></alternatives></inline-formula> state of <inline-formula><tex-math id="M10">\begin{document}$ {\text{N}}_{2}^{+} $\end{document}</tex-math><alternatives><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="19-20220734_M10.jpg"/><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="19-20220734_M10.png"/></alternatives></inline-formula> are calculated by the internal contraction multi reference configuration interaction (icMRCI) method, with Davidson correction taken into consideration. According to the results of molecular structures, we present the partition function in a temperature range of 100–40000 K and the opacities at different temperatures (295, 500, 1000, 2000, 2500, 5000 and 10000 K) under a fixed pressure of 100 atm. It is found that the populations of excited states increase with temperature increasing, as a result, the wavelength range of opacity also increases and band boundaries for different transitions gradually become obscure. In comparison with the cases of N<sub>2</sub> with the same pressure and temperature, significant discrepancies are found in the wavelength ranges and structures of opacity of <inline-formula><tex-math id="M1119">\begin{document}$ {\text{N}}_{2}^{+} $\end{document}</tex-math><alternatives><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="19-20220734_M1119.jpg"/><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="19-20220734_M1119.png"/></alternatives></inline-formula> for the present work. The influence of temperature on the opacity of <inline-formula><tex-math id="M11">\begin{document}$ {\text{N}}_{2}^{+} $\end{document}</tex-math><alternatives><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="19-20220734_M11.jpg"/><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="19-20220734_M11.png"/></alternatives></inline-formula> is studied systematically in the present work, which is expected to provide theoretical and data support for astrophysics.

Theoretical study on spectroscopic properties of 8 Λ-S and 23 Ω states for BH molecule

In this work, the potential energy curves of eight low electronic states (X<sup>1</sup>Σ<sup>+</sup>, a<sup>3</sup>Π, A<sup>1</sup>Π, b<sup>3</sup>Σ<sup>-</sup>, 2<sup>3</sup>Π, 1<sup>3</sup>Σ<sup>+</sup>, 1<sup>5</sup>Σ<sup>-</sup>, and 1<sup>5</sup>Π) and twenty-three Ω states of BH molecule, and the transition dipole moments among the <inline-formula><tex-math id="M10">\begin{document}$ {\text{X}}{}^{\text{1}}{\Sigma}_{{{\text{0}}^ + }}^ + $\end{document}</tex-math><alternatives><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="10-20220038_M10.jpg"/><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="10-20220038_M10.png"/></alternatives></inline-formula>, <inline-formula><tex-math id="M11">\begin{document}$ {{\text{a}}^{\text{3}}}{\Pi_{{{\text{0}}^ + }}} $\end{document}</tex-math><alternatives><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="10-20220038_M11.jpg"/><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="10-20220038_M11.png"/></alternatives></inline-formula>, a<sup>3</sup>Π<sub>1</sub>, a<sup>3</sup>Π<sub>2</sub>, and A<sup>1</sup>Π<sub>1</sub> states are calculated by using the internally contracted multireference configuration interaction (icMRCI) method. In order to obtain the accurate potential energy curve, the errors caused by single and double electron excitation, core-valence correlation effects, relativistic effects and basis set truncation are corrected. The spectral and transition data of BH molecule are in good agreement with the available theoretical and experimental data. The calculation results show that the A<sup>1</sup>Π<sub>1</sub>(<i>υ′</i> = 0-2, <i>J′</i> = 1, +) →<inline-formula><tex-math id="M12">\begin{document}$ {\text{X}}{}^{\text{1}}{\Sigma}_{{{\text{0}}^ + }}^ + $\end{document}</tex-math><alternatives><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="10-20220038_M12.jpg"/><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="10-20220038_M12.png"/></alternatives></inline-formula>(<i>υ′′</i> = 0-2, <i>J′′</i> = 1, –) transition has large Einstein <i>A</i>-coefficient, weighted absorption oscillator strength, and highly diagonal vibrational branching ratio<i> R</i><sub><i>υ′υ′′</i></sub>, and the excited state A<sup>1</sup>Π<sub>1</sub>(<i>υ′</i> = 0, 1) have short spontaneous radiation lifetimes. Moreover, the effects of <inline-formula><tex-math id="M13">\begin{document}$ {{\text{a}}^{\text{3}}}{\Pi_{{{\text{0}}^ + }}} $\end{document}</tex-math><alternatives><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="10-20220038_M13.jpg"/><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="10-20220038_M13.png"/></alternatives></inline-formula>and a<sup>3</sup>Π<sub>1</sub> states on A<sup>1</sup>Π<sub>1</sub>(<i>υ′</i> = 0) ↔ <inline-formula><tex-math id="M14">\begin{document}$ {\text{X}}{}^{\text{1}}{\Sigma}_{{{\text{0}}^ + }}^ + $\end{document}</tex-math><alternatives><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="10-20220038_M14.jpg"/><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="10-20220038_M14.png"/></alternatives></inline-formula>(<i>υ′′</i> = 0) cycle transition can be ignored. Therefore, according to the A<sup>1</sup>Π<sub>1</sub>(<i>υ′</i><sub> </sub>= 0-1, <i>J′</i> = 1, +) ↔ <inline-formula><tex-math id="M15">\begin{document}$ {\text{X}}{}^{\text{1}}{\Sigma}_{{{\text{0}}^ + }}^ + $\end{document}</tex-math><alternatives><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="10-20220038_M15.jpg"/><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="10-20220038_M15.png"/></alternatives></inline-formula>(<i>υ′′</i><sub> </sub>= 0-3, <i>J</i>′′ = 1, –) cycle transition, we propose to apply one main cooling laser (<i>λ</i><sub>00</sub> = 432.45 nm) and two repumping lasers (<i>λ</i><sub>10</sub> = 479.67 nm and <i>λ</i><sub>21</sub> = 481.40 nm) to laser cooling BH molecules, and evaluation of the cooling effect.

An ab initio study of the rovibronic spectrum of sulphur monoxide (SO): diabatic vs. adiabatic representation.

We present an ab initio study of the rovibronic spectra of sulphur monoxide (32S16O) using internally contracted multireference configuration interaction (ic-MRCI) method and aug-cc-pV5Z basis sets. It covers 13 electronic states X3Σ-, a1Δ, b1Σ+, c1Σ-, A''3Σ+, A'3Δ, A3Π, B3Σ-, C3Π, d1Π, e1Π, C'3Π, and (3)1Π ranging up to 66 800 cm-1. The ab initio spectroscopic model includes 13 potential energy curves, 23 dipole and transition dipole moment curves, 23 spin-orbit curves, and 14 electronic angular momentum curves. A diabatic representation is built by removing the avoided crossings between the spatially degenerate pairs C3Π-C'3Π and e1Π-(3)1Π through a property-based diabatisation method. We also present non-adiabatic couplings and diabatic couplings for these avoided crossing systems. All phases for our coupling curves are defined, and consistent, providing the first fully reproducible spectroscopic model of SO covering the wavelength range longer than 147 nm. Finally, an ab initio rovibronic spectrum of SO is computed.

Spectral characteristics of low excited state of strontium monobromide molecule

The electronic structures and single point energy of 14 lowest electronic states of <sup>88</sup>Sr<sup>79</sup>Br molecule are optimized by using the internal contraction multi-reference configuration interaction method and relativistic effective core pseudo-potential basis. Because <sup>88</sup>Sr<sup>79</sup>Br molecule belongs to heavy element system, the single point energy must be corrected to obtain more accurate spectral parameters. Therefore, Davidson is introduced to correct the energy inconsistency, nuclear valence correlation is used to correct the electron correlation effect of inner shell and valence shell, and the relativistic scalar effect is corrected by calculating the third-order Douglas-Kroll-Hess Hamilton single electron integral. According to the single point energy calculated by the modified optimization, the potential energy curves, electric dipole moments, and transition dipole moments of 14 lowest electronic states are obtained. Using the latest LEVEL8.0 program to fit the modified potential energy curve, the spectral constants, molecular constants and vibration energy levels of 5 lowest bound states of <sup>88</sup>Sr<sup>79</sup>Br molecule are given. In order to explain the changing trend of spectral constants of homologous compounds, the spectral parameters of each compound are compared and analyzed in this paper. At the same time, the vibration energy levels and molecular constants of <sup>88</sup>Sr<sup>81</sup>Br molecule are also fitted and calculated for analyzing the influence of isotopes. The comparative analysis shows that the results of <sup>88</sup>Sr<sup>79</sup>Br molecule are in better agreement with the experimental values. Finally, the Franck-Condon factors are gained by fitting the optimized single point energy and transition dipole moment of <sup>88</sup>Sr<sup>79</sup>Br molecule. The transition band with the largest factor and obvious diagonalization is selected by analyzing the Franck-Condon factor of each transition band, and whether it meets the conditions for selecting laser cooling molecular system is judged. The radiation lifetimes of the transitions from the lowest two excited states to the ground state are calculated by combining the transition dipole moment, Franck-Condon factor, single point energy and vibration energy level of each electronic state. The results of this paper are in good agreement with the experimental values, which shows that the method in this paper is reliable. These spectral characteristic parameters provide theoretical support for further experimental measurement and construction of molecular laser cooling scheme of <sup>88</sup>Sr<sup>79</sup>Br molecule.

Configuration Interaction Methods to Predictions on Photophysical Properties of Organic Materials

Configuration Interaction Methods to Predictions on Photophysical Properties of Organic Materials

Calculations of relativistic, correlation, nuclear and quantum-electrodynamics corrections to the energies and ionization potentials of the ground state of lithium-like ions

This paper presents all the leading contributions to the relativistic binding energies and ionization potentials of the ground state of lithium-like ions with a nuclear charge in the range Z=3-20. Correlation, relativistic and quantum-electrodynamics corrections as well as the contributions due to the finite size of the nucleus (the field shift) and finite mass of the nucleus (the recoil effect) are evaluated. Relativistic calculations are performed by means of the configuration-interaction method in the basis of the Dirac-Fock-Sturm orbitals using the Dirac-Coulomb-Breit Hamiltonian. Keywords: Li-like ions, ionization potential, relativistic calculations, configuration interaction, electron correlations, Breit interaction, field shift, nuclear recoil effect, QED corrections

Расчеты релятивистских, корреляционных, ядерных и квантово-электродинамических поправок к энергиям и потенциалам ионизации основного состояния литиеподобных ионов

This paper presents all the leading contributions to the relativistic total energies and ionization potentials of the ground state of lithium-like ions with a nuclear charge in the range Z = 3 − 20. Correlation, relativistic and quantum-electrodynamics corrections as well as contributions due to the finite size of the nucleus (field shift) and finite mass of the nucleus (recoil effect) are evaluated. Relativistic calculations are performed by means of the configuration-interaction method in the basis of the Dirac-Fock-Sturm orbitals using the Dirac-Coulomb-Breit Hamiltonian.

Multicomponent heat-bath configuration interaction with the perturbative correction for the calculation of protonic excited states.

In this study, we extend the multicomponent heat-bath configuration interaction (HCI) method to excited states. Previous multicomponent HCI studies have been performed using only the variational stage of the HCI algorithm as they have largely focused on the calculation of protonic densities. Because this study focuses on energetic quantities, a second-order perturbative correction after the variational stage is essential. Therefore, this study implements the second-order Epstein-Nesbet correction to the variational stage of multicomponent HCI for the first time. Additionally, this study introduces a new procedure for calculating reference excitation energies for multicomponent methods using the Fourier-grid Hamiltonian (FGH) method, which should allow the one-particle electronic basis set errors to be better isolated from errors arising from an incomplete description of electron-proton correlation. The excited-state multicomponent HCI method is benchmarked by computing protonic excitations of the HCN and FHF- molecules and is shown to be of similar accuracy to previous excited-state multicomponent methods such as the multicomponent time-dependent density-functional theory and equation-of-motion coupled-cluster theory relative to the new FGH reference values.

Excellent Ultracold Molecular Candidates From Group VA Hydrides: Whether Do Nearby Electronic States Interfere?

By means of highly accurate ab initio calculations, we identify two excellent ultracold molecular candidates from group VA hydrides. We find that NH and PH are suitable for the production of ultracold molecules, and the feasibility and advantage of two laser cooling schemes are demonstrated, which involve different spin-orbit states ( and ). The internally contracted multireference configuration interaction method is applied in calculations of the six low-lying Λ-S states of NH and PH with the spin-orbit coupling effects included, and excellent agreement is achieved between the computed and experimental spectroscopic data. We find that the locations of crossing point between the and states of NH and PH are higher than the corresponding v′ = 2 vibrational levels of the state indicating that the crossings with higher electronic states would not affect laser cooling. Meanwhile, the extremely small vibrational branching loss ratios of the → transition for NH and PH (NH: 1.81 × 10–8; PH: 1.08 × 10–6) indicate that the intermediate electronic state will not interfere with the laser cooling. Consequently, we construct feasible laser-cooling schemes for NH and PH using three lasers based on the → transition, which feature highly diagonal vibrational branching ratio (NH: 0.9952; PH: 0.9977), the large number of scattered photons (NH: 1.04×105; PH: 8.32×106) and very short radiative lifetimes (NH: 474 ns; PH: 526 ns). Our work suggests that feasible laser-cooling schemes could be established for a molecular system with extra electronic states close to those chosen for laser-cooling.

Two-Component Multireference Restricted Active Space Configuration Interaction for the Computation of L-Edge X-ray Absorption Spectra.

X-ray absorption spectroscopy is a powerful probe of local electronic and nuclear structures, providing insights into chemical processes. The theoretical prediction and interpretation of metal L-edge X-ray absorption spectra are complicated by both relativistic effects, including spin-orbit coupling and the multiconfigurational nature of the states involved. This work details an exact two-component multireference restricted active space (RAS) configuration interaction scheme that uses an exact two-component state-averaged complete active space self-consistent-field method, which includes the spin-orbit coupling in a variational manner, for the accurate description of the electronic structure before using a RAS configuration interaction method to describe the core excited states of the X-ray spectrum. Benchmark calculations are presented for a series of iron-containing complexes, with results showing key features of the spectrum being reproduced, including ligand-to-metal charge transfer and shake-up excitations.

Destruction of AlF: a quantum study of its ground-state photodissociation

ABSTRACTPhotodissociation by ultraviolet photons is the key destruction pathway for aluminium monofluoride (AlF) in the envelope of the carbon star IRC +10216 from the stellar photosphere up to the outer layers. However, there is no available photodissociation data for AlF, which hampers the prediction of the abundances of Al-bearing molecules in astrochemical models. Here, we present an ab initio study of AlF photodissociation. Potential energy curves of seven singlet states for AlF were computed by the internally contracted multireference single and double configuration-interaction method and aug-cc-pCV5Z-DK basis set, along with the transition dipole moments from excited singlet states to the ground state. State-resolved cross sections for the direct photodissociation from 36 349 ground rovibrational levels ( υ″≤120, J″≤360) to six singlet excited states were calculated by the quantum mechanical method. We found that the 21Π←X 1Σ+, 31Π←X 1Σ+, and 41Π←X 1Σ+ transitions have extremely strong absorption for lower wavelengths, especially between the Lyman and Lyman α ones. Photodissociation cross sections in local thermal equilibrium were estimated for gas temperatures from 500 to 20 000 K. Finally, the cross sections were utilized to calculate the photodissociation rates in the interstellar and blackbody radiation fields. The obtained photodissociation cross sections and rates can be used to determine the abundance of AlF in astrochemical models.

Exploiting the nearsightedness principle within the framework of the anti‐Hermitian contracted Schrödinger equation

AbstractThis work exploits the Kohn nearsightedness principle in the algorithms arising from the anti‐Hermitian contracted Schrödinger equation. The procedure provides the implementation of approximations yielding a considerable saving of computational costs in descriptions of N‐electron molecular systems by means of that technique. We report energies, at correlated level, of linear hydrogen chains designed at different geometries, so that we can analyze the strength of the interactions between first‐, second‐, third‐, fourth‐, and so forth neighbor atoms. Using localized molecular orbital basis sets, we observe rapid decays in the values of the elements of the reduced‐density‐matrix cumulant matrices, beyond a cut‐off radius, which justify the proposed approximations. The results, in terms of energies and reduced density matrices, have been compared with those obtained from the full configuration interaction method, showing the usefulness of the nearsightedness principle in this methodology.

Removing the Deadwood from DFT/MRCI Wave Functions: The p-DFT/MRCI Method.

The combined density functional theory and multireference configuration interaction (DFT/MRCI) method is a powerful tool for the calculation of excited electronic states of large molecules. There exists, however, a large amount of superfluous configurations in a typical DFT/MRCI wave function. We show that this deadwood may be effectively removed using a simple configuration pruning algorithm based on second-order Epstein-Nesbet perturbation theory. The resulting method, which we denote p-DFT/MRCI, is shown to result in orders of magnitude saving in computational timings, while retaining the accuracy of the original DFT/MRCI method.

Exploring the low-lying electronic states of AsO including spin–orbit interaction

In this paper, the multireference configuration interaction method (MRCI) combined with the Davidson correction (+Q) is used to study the high-level ab initio calculation of AsO electronic states. The potential energy curves (PECs) of 27 Λ-S states and 18 Ω states related to the three lowest dissociation limits are obtained. According to these PECs, the spectroscopic constants of Λ-S and Ω states can be calculated, which is little different from the previous experimental values. The dipole moments (DMs) of the Λ-S state is also calculated. In addition, the transition properties of several transitions are calculated, including the transition dipole moments (TDMs), Franck-Condon factors (FCFs) and spontaneous radiative lifetimes of Λ-S state. This work should improve our understanding of the electronic structure and spectroscopic information of AsO.

Benchmarking Multiconfiguration Dirac–Hartree–Fock Calculations for Astrophysics: Si-like Ions from Cr xi to Zn xvii

Abstract The multiconfiguration Dirac–Hartree–Fock (MCDHF) and relativistic configuration interaction methods are used to provide excitation energies, lifetimes, and radiative transition data for the 604 (699, 702, 704, 704, 704, and 699) lowest levels of the 3s 23p 2, 3s3p 3, 3s 23p3d, 3p 4, 3s3p 23d, 3s 23d 2, 3p 33d, 3s3p3d 2, 3s3d 3, 3p3d 3, 3p 23d 2, 3s 23p4s, 3s 23p4p, 3s 23p4d, 3s 23p4f, 3s3p 24s, 3s3p 24p, 3s3p 24d, 3s3p 24f, 3s 23d4s, 3s 23d4p, 3p 34s, 3p 34p, 3s3p3d4s, 3s 23p5s, and 3s 23p5p configurations in Cr xi, (Mn xii, Fe xiii, Co xiv, Ni xv, Cu xvi, and Zn xvii). Previous line identifications of Fe xiii and Ni xv in the EUV and X-ray wavelength ranges are reviewed by comprehensively comparing the MCDHF theoretical results with available experimental data. Many recent identifications of Fe xiii and Ni xv lines are confirmed, and several new identifications for these two ions are proposed. A consistent atomic data set with spectroscopic accuracy is provided for the lowest hundreds of levels for Si-like ions of iron-group elements of astrophysical interest, for which experimental values are scarce. The uncertainty estimation method suggested by Kramida, applied to the comparison of the length and velocity line strength values, is used for ranking the transition data. The correlation of the latter with the gauge dependency patterns of the line strengths is investigated.

Relativistic Configuration-Interaction and Perturbation Theory Calculations for Heavy Atoms

Heavy atoms present challenges to atomic theory calculations due to the large number of electrons and their complicated interactions. Conventional approaches such as calculations based on Cowan’s code are limited and require a large number of parameters for energy agreement. One promising approach is relativistic configuration-interaction and many-body perturbation theory (CI-MBPT) methods. We present CI-MBPT results for various atomic systems where this approach can lead to reasonable agreement: La I, La II, Th I, Th II, U I, Pu II. Among atomic properties, energies, g-factors, electric dipole moments, lifetimes, hyperfine structure constants, and isotopic shifts are discussed. While in La I and La II accuracy for transitions is better than that obtained with other methods, more work is needed for actinides.

Large-scale atomic data calculations in Ce V – X ions for application to early kilonova emission from neutron star mergers

ABSTRACT New radiative parameters (wavelengths, transition probabilities, and oscillator strengths) are reported in the present paper for a large number of spectral lines in moderately charged cerium ions, from Ce V to Ce X. These results were obtained through large-scale atomic structure calculations carried out using three different and independent theoretical approaches, namely the relativistic Hartree–Fock method, including core-polarization corrections (HFR + CPOL), the multiconfiguration Dirac–Hartree–Fock method, and the Particle-Hole Configuration Interaction (PH-CI) method implemented in the AMBiT code. The accuracy of the results was assessed through detailed comparisons between the data deduced from these methods and with the few theoretical and experimental data previously published. For the six cerium ions considered, the most complete and reliable sets of transition wavelengths and rates were then used to calculate the expansion opacities characterizing the early phases of kilonovae following neutron star mergers, i.e. for typical conditions corresponding to temperatures T > 20 000 K, a density ρ = 10−10 g cm−3 and a time after the merger t = 0.1 d.

Theoretical level energies and transition data for 4p64d8, 4p54d9 and 4p64d74f configurations of W[formula omitted] ion

The ab initio quasirelativistic approach developed specifically for the calculation of spectral parameters of highly charged ions was used to derive transition data for the Ru-like tungsten ion W30+. The configuration interaction method was applied to include electron correlation effects. The relativistic effects were taken into account in the Breit–Pauli approximation. The level energies, radiative lifetimes τ, Landé g-factors were determined for the ground configuration 4p64d8 and two excited configurations 4p54d9 and 4p64d74f. The radiative transition wavelengths λ and emission transition probabilities A for the electric dipole, electric quadrupole, electric octupole, magnetic dipole, and magnetic quadrupole transitions among the levels of these configurations were generated.

Accurate energies of transition metal atoms, ions, and monoxides using selected configuration interaction and density-based basis-set corrections.

The semistochastic heat-bath configuration interaction method is a selected configuration interaction plus perturbation theory method that has provided near-full configuration interaction (FCI) levels of accuracy for many systems with both single- and multi-reference character. However, obtaining accurate energies in the complete basis-set limit is hindered by the slow convergence of the FCI energy with respect to basis size. Here, we show that the recently developed basis-set correction method based on range-separated density functional theory can be used to significantly speed up basis-set convergence in SHCI calculations. In particular, we study two such schemes that differ in the functional used and apply them to transition metal atoms and monoxides to obtain total, ionization, and dissociation energies well converged to the complete-basis-set limit within chemical accuracy.