Configuration Interaction Study Research Articles

Multi-component configuration interaction study for positron–molecule compounds: benchmark calculations of positron binding in polar and non-polar molecules

Multi-component configuration interaction study for positron–molecule compounds: benchmark calculations of positron binding in polar and non-polar molecules

Non-orthogonal Configuration Interaction Study on the Effect of Thermal Distortions on the Singlet Fission Process in Photoexcited Pure and B,N-Doped Pentacene Crystals.

The present computational work analyzes singlet fission (SF) as a pathway for multiplication of photogenerated excitons in crystalline polyacenes. Our study explores the well-known crystalline pentacene (C22H14) and the prospective and potentially interesting doped B,N-pentacene (BC20NH14). At the molecular level, the singlet fission process involves a pair of neighboring molecules and is based on the coupling between an excited singlet state (S1S0) and two singlet-coupled triplets (1T1T1), which, typically, is influenced by an intermolecular charge transfer state. Taking data from periodic density functional theory and ab initio wave function calculations, we applied the non-orthogonal configuration interaction method to determine electronic coupling parameters. The comparison of the results for both equilibrium structures reveal smaller SF coupling for pentacene than for B,N-pentacene by a factor of ∼5. Introduction of the dynamic behavior to the crystals (vibrations, thermal motion) provides a more realistic picture of the effect of the disorder at the molecular level on the SF efficiency. The coupling values associated to out-of-equilibrium structures show that most of the S1S0/1T1T1 couplings remain virtually constant or slightly increase for pentacene when molecular disorder is introduced. Homologous calculations on B,N-pentacene show a generalized decrease in the coupling values, notably if large phonon displacements are considered. A few of the structures analyzed feature much larger SF coupling if some distortion results in (nearly) degenerate charge transfer and excited singlet and triplet states. For these particular situations, an acceleration of the SF process could occur although in competition with electron-hole separation as an alternative pathway.

Exponentially Correlated Hylleraas–Configuration Interaction Studies of Atomic Systems. III. Upper and Lower Bounds to He-Sequence Oscillator Strengths for the Resonance 1S→1P Transition

The exponentially correlated Hylleraas–configuration interaction method (E-Hy-CI) is a generalization of the Hylleraas–configuration interaction method (Hy-CI) in which the single rij of an Hy-CI wave function is generalized to a form of the generic type rijνije−ωijrij. This work continues the exploration, begun in the first two papers in this series (on the helium atom and on ground and excited S states of Li II), of whether wave functions containing both linear and exponential rij factors converge more rapidly than either one alone. In the present study, we examined not only 1s2 1S states but 1s2p 1P states for the He I, Li II, Be III, C V and O VII members of the He isoelectronic sequence as well. All 1P energies except He I are better than previous results. The wave functions obtained were used to calculate oscillator strengths, including upper and lower bounds, for the He-sequence lowest (resonance) 1S→1P transition. Interpolation techniques were used to make a graphical study of the oscillator strength behavior along the isoelectronic sequence. Comparisons were made with previous experimental and theoretical results. The results of this study are oscillator strengths for the 1s2 1S→ 1s2p1P He isoelectronic sequence with rigorous non-relativistic quantum mechanical upper and lower bounds of (0.001–0.003)% and probable precision ≤ 0.0000003, and were obtained by extending the previously developed E-Hy-CI formalism to include the calculation of transition moments (oscillator strengths).

A spin–orbit configuration interaction study of the low-lying electronic states of the diatomic lithium antimonide cation

High-level ab initio calculations were performed to determine the structural features, electronic characteristics and transitional properties of LiSb+, which is a hitherto experimentally unknown diatomic cation. We acquired and evaluated the potential energy curves, spectroscopic constants and vibrational energy levels for low-lying Λ-S electronic states and their related Ω states. The spin–orbit coupling effect has a slight impact on these states. Transitional properties, such as transition dipole moments, Einstein coefficients, Franck–Condon factors and vibrational branching ratios, as well as the radiative lifetimes of transitions from excited Ω states to the ground state, have been identified and discussed. We anticipate that these prognostic results will act as guidelines for future research.

Spin–orbit configuration interaction study of spectral properties of PbO

Relativistic calculations of the structural and spectral properties of the PbO molecule can provide fundamental information about the importance of a proper treatment of angular momentum coupling among electrons in order to achieve accurate computational results for spectral properties. Specifically, the nature of these couplings in PbO is expected to be intermediate between the LS- and jj-coupling limits because of its light/heavy element composition. This article reports potential energy curves, transition energies, electric dipole transition moments, permanent dipole moments and spectroscopic constants of PbO calculated using a multireference single plus double excitations spin–orbit configuration interaction approach in the context of relativistic effective core potentials and their concomitant spin–orbit coupling operators. The calculated results are in general agreement with both available experimental results as well as earlier calculations. New values for properties of excited states are also reported. It is noteworthy that certain properties show larger deviations from previous calculations. These deviations are attributed to direct and indirect relativistic effects resulting from diatomic electron–electron angular momentum coupling effects, which are included consistently in the calculations reported herein.

Effects of electronic correlation on the high harmonic generation in helium: A time-dependent configuration interaction singles vs time-dependent full configuration interaction study.

In this paper, we investigate the effects of full electronic correlation on high harmonic generation in the helium atom subjected to laser pulses of extremely high intensity. To do this, we perform real-time propagations of helium atom wavefunction using quantum chemistry methods coupled to Gaussian basis sets. Calculations are performed within the real-time time-dependent configuration interaction framework at two levels of theory: time-dependent configuration interaction with single excitations (uncorrelated method) and time-dependent full configuration interaction (fully correlated method). The electronic wavefunction is expanded in Dunning basis sets supplemented with functions adapted to describing highly excited and continuum states. We also compare the time-dependent configuration interaction results with grid-based propagations of the helium atom within the single-active-electron approximation. Our results show that when including the dynamical electron correlation, a noticeable improvement to the description of high harmonic generation (HHG) can be achieved in terms of, e.g., a more constant intensity in the lower energy part of the harmonic plateau. However, such effects can be captured only if the basis set used suffices to reproduce the most basic features, such as the HHG cutoff position, at the uncorrelated level of theory.

Configuration interaction study on excited electronic states and radiative lifetimes of SnI including spin-orbit coupling

In this work, the high-level multireference configuration interaction (MRCI) method is used to accurately calculate the electronic structure of SnI. In order to guarantee the computational precision, the Davidson correction (+Q), core-valence (CV) electrons correlations and spin-orbit coupling (SOC) effect are also considered. According to the calculated potential energy curves (PECs) of the Λ-S states and Ω states, the spectroscopic constants of the bound states are estimated. The interaction of crossing states are investigated, and with the aid of calculated SO matrix elements, the predissociation pathways of 14Σ− state are revealed. In addition, the transition dipole moments (TDMs) and Franck-Condon factors (FCFs) from the excited states to the ground state are determined. Finally, the radiative lifetimes of bound states are calculated, and the influences of SOC effect on radiative lifetimes are illuminated.

Configuration interaction study on low-lying states of AlCl molecule* *Project supported by the National Key Research and Development Program of China (Grant No. 2017YFA0403300), the National Natural Science Foundation of China (Grant Nos. 11874177, 11874179, and 11574114), the Natural Science Foundation of Jilin Province, China (Grant No. 20180101289JC), and the High Performance Computing Center of Jilin University and High Performance

High-level ab initio calculations of the Λ–S states for aluminum monoiodide (AlCl) molecule are performed by utilizing the explicitly correlated multireference configuration interaction (MRCI-F12) method. The Davidson correction and scalar relativistic correction are investigated in the calculations. Based on the calculation by the MRCI-F12 method, the spin–orbit coupling (SOC) effect is investigated with the state-interacting technique. The adiabatic potential energy curves (PECs) of the 13 Λ–S states and 24 Ω states are calculated. The spectroscopic constants of bound states are determined, which are in accordance with the results of the available experimental and theoretical studies. Finally, the transition properties of 0+(2)–X0+, 1(1)–X0+, and 1(2)–X0+ transitions are predicted, including the transition dipole moments (TDMs), Franck–Condon factors (FCFs), and the spontaneous radiative lifetimes.

A multireference configuration interaction study with singles and doubles of some mesoionic rings: reaction and activation free energies for the ring‐opening reaction

AbstractFor the first time, multireference configuration interaction with singles and doubles (MR‐CISD) calculations (including extensivity corrections, MR‐CISD+Q) have been performed to study the ring‐opening reactions of the following mesoionic rings and their 2, 3, and 4 methyl‐substituted derivatives: (a) 1,3‐oxazol‐5‐one, (c) 1,3‐oxazol‐5‐thiolate, and (d) 1,3‐thiazol‐5‐thiolate. The ring‐opening reaction of the parent 1,3‐thiazol‐5‐one mesoionic ring (b) has also been studied. The effect of methyl and S replacement on the reaction and activation free energies (ΔG and ΔG†, respectively) is studied. For a, the effect of methyl replacement on C2 is almost negligible, while on N3 and C4, it is significantly larger, especially in the latter position. The open structure (ketene form) of a is considerably more stable, and the replacement of the exocyclic O by S stabilizes the ketene tautomer even more and increases ΔG† considerably. On the other hand, replacement of the endocyclic O by S (yielding b) completely prevents the formation of the open structure, while replacement of both endo and exo atoms strongly stabilizes the cyclic structure and leads to a remarkably high value of ΔG†. In some cases, the relative polarity of the stationary points is used to estimate how ΔG and ΔG† are expected to change as one goes from the gas phase to aprotic polar solvents. A linear correlation between the multiconfigurational character of the mesoionic rings and ΔG† has been observed, and such correlation is used to estimate the ΔG† values for the methyl‐substituted c and d. The largest barrier (13.78 kcal/mol) has been obtained for the 4‐methyl‐1,3‐thiazol‐5‐thiolate (4‐m‐d).

A comparative multi‐reference configuration interaction study of the low‐lying states of two thione isomers of thiophenol

AbstractMulti‐reference configuration interaction, MR‐CI (including extensivity corrections, named +Q), calculations were performed on the S0–S3 states of cyclohexa‐2,4‐diene‐1‐thione (thione 24) and cyclohexa‐2,5‐diene‐1‐thione (thione 25), which are thione isomers of thiophenol. Several types of uncontracted MR‐CIS and MR‐CISD wavefunctions were employed, comprising MR‐CI expansions as large as ~365 × 106 configuration state functions. The nature of the studied excited states was characterized. Vertical excitation energies (ΔE) and oscillator strengths (f) were computed. The most intense transitions (S0 → S2 for 24 and S0 → S3 for 25) did not change with the wavefunction, although a variation as large as ~1 eV was obtained for the S3 state of 24, at the highest (MR‐CI+Q) level. On the other hand, ΔE changed at most by ~0.56 eV for 25 as the wavefunction changes, at the same level. The S1 state of both thiones was found to have nπ* character and is in the visible region. For 24, S2 and S3 are ππ* and nπ* states, respectively, while for 25 the reverse order is obtained. S2 and S3 are in the range ~3.5 to 5.2 eV, again at the highest level. It is the first time that the excited states of the title molecules are studied. The computed results agree with the experimental onset of photoreactions of thiones 24 and 25 found by Reva et al (Phys. Chem. Chem. Phys., 2015, 17, 4888).

The configuration interaction study on the low-lying electronic states of AsF

High-level ab initio calculation on the 22 Λ-S electronic states of AsF has been performed with all-electron Gaussian basis sets and internally contracted multireference configuration interaction method plus Davidson correction (icMRCI+Q) and scalar relativistic effect. The spin-orbit coupling (SOC) has been investigated in the calculations by using the Breit-Pauli operator. After considering the SOC, the 22 Λ-S states of AsF split into 51 Ω states related to the lowest five dissociation limits. The spectroscopic constants of the bound states were obtained, which are found in better agreement with available experimental and theoretical results. Based on the computed potential energy curves (PECs), permanent dipole moments (PDMs), transition dipole moments (TDMs), Franck-Condon factors (FCFs) and radiative lifetimes have been acquired. This work should enhance our understanding of the electronic structure and spectroscopy information of AsF radical.

The electronically excited states of cyclooctatetraene-An analysis of the vacuum ultraviolet absorption spectrum by ab initio configuration interaction methods.

A new synchrotron-based study of the vacuum ultraviolet (VUV) absorption spectrum for cyclooctatetraene (COT) shows a series of broad peaks. A significant sharp structure was extracted from the strongest band between 5.9 and 6.3 eV by fitting this range of the spectrum to a polynomial; the regular residuals show a set of sharp peaks. Comparison of this region of the VUV with the photoelectron spectrum demonstrates the presence of several Rydberg states, all based on the lowest observed ionization energy ionic state. The UV onset contains a broad band in the range 4.0 eV-5.3 eV. Theoretical vertical excitation energies, determined by configuration interaction (CI) studies at the multireference multiroot singles and doubles CI level, enabled interpretation of the principal absorption bands of the VUV spectrum. Adiabatic excitation energies (AEEs) for several singlet and triplet valence states (V) were evaluated by multiconfiguration self-consistent field methods. Theoretical Rydberg series AEEs were obtained by use of extremely diffuse Gaussian orbitals in highly correlated wave-functions. The second moments of the charge distribution identify which roots are valence or Rydberg states. A contrast was found between some density functional methods and Hartree-Fock (HF) wave-functions during single-excitation CI, when degenerate orbitals were involved in the leading configurations. The 7a16e* state contained the expected 8-membered ring in the density functional theory calculations. The HF wave-functions led to a 1,5-cross-ring interaction which converged on a singlet excited state of a bicyclo[3,3,0]octatriene; this is reminiscent of the photochemical conversion of COT to semibullvalene.

The low-lying electronic states of HfO2− and HfO2: A symmetry adapted cluster–configuration interaction (SAC-CI) study

The low-lying doublet states of the HfO2− anion and low-lying triplet excited states of the HfO2 molecule were studied using the SAC-CI method. The vertical excitation spectrum of HfO2− was calculated. Four valence-bound states (X2A1, 12B1, 22A1, and 12B2(II)) and one dipole-bound state (2A1(DB)) of HfO2− were found. The vertical electron detachment energies (VDEs) from the ground electronic state of HfO2− to the triplet excited states of HfO2 were obtained. These VDEs were compared with previous photoelectron spectra of HfO2−, and possible candidate states for the unassigned bands were found. The equilibrium geometries of the valence-bound states of HfO2− and some selected triplet excited states of HfO2 were optimized. The adiabatic relative energies of these electronic states were obtained. Density functional theory (BPW91) was also applied to compute some electronic states of HfO2− and HfO2 for comparison.

The low-lying triplet electronic excited states of TiO2 and ZrO2: A symmetry adapted cluster–configuration interaction (SAC-CI) study

The vertical excitation energies and electron detachment energies to the low-lying triplet excited states of TiO2 and ZrO2 were calculated at the SAC-CI/aug-cc-pVTZ levels. The vertical electron detachment energies to the triplet excited states of TiO2 were compared with previous photoelectron spectra. Possible candidate states for the unassigned bands in the previous photoelectron spectrum were found. Several triplet excited states of TiO2 and ZrO2 were optimized at the SAC-CI/aug-cc-pVDZ and SAC-CI/def2-SVPD levels, respectively. The adiabatic excitation energies and electron detachment energies to the selected triplet states were obtained by single-point calculations at the SAC-CI/def2-TZVPPD level. Density functional theory (BPW91/aug-cc-pVTZ) was also applied to study some of the triplet states for comparison. The calculated electron detachment energies and optimized geometries of the triplet excited states should be useful for studying the photoelectron spectra of TiO2− and ZrO2−.

Application of the Landau-Zener-Stückelberg-Majorana dynamics to the electrically driven flip of a hole spin

An idea of employing the Landau-Zener-St\"uckelberg-Majorana (LZSM) dynamics to flip a spin of a single ground state hole is introduced and explored by a time-dependent simulation. This configuration interaction study considers a hole confined in a quantum molecule formed in InSb $\langle111\rangle$ quantum wire by application of an electrostatic potential. An up-down spin-mixing avoided crossing is formed by non-axial terms in the Kohn-Luttinger Hamiltonian and the Dresselhaus spin-orbit one. Manipulation of the system is possible by dynamic change of external vertical electric field, which enables the consecutive driving of the hole through two anticrossings. Moreover, a simple model of the power-law type noise that impedes the precise electric control of the system is included in the form of Random Telegraph Noise to estimate the limitations of the working conditions. We show that in principle the process is possible, but it requires a precise control of parameters of the driving impulse.

The low-lying doublet electronic excited states of ZrO2−: A symmetry adapted cluster–configuration interaction (SAC-CI) study

The low-lying doublet excited states of ZrO2− were studied using the SAC-CI method. The vertical excitation spectrum of ZrO2− was calculated and compared with that of TiO2−. Similar to that for TiO2−, ZrO2− also have a dipole-bound state. The ground electronic state (X2A1) and the excited states having bound characters (22A1, 12B1, and dipole-bound states) were optimized to C2v structures. The adiabatic electronic affinity of ZrO2 and the adiabatic excitation energies of the three bound excited states were obtained at the SAC-CI level.

Multireference configuration interaction study on the ground and excited electronic states of the AlO+ molecule

High-level ab initio calculations on the electronic states of AlO+ cation have been performed with the explicitly correlated multi-reference configuration interaction (MRCI-F12) method. The potential energy curves (PECs) of 24 electronic states have been obtained, most of which are reported for the first time. From the computed PECs, the precise spectroscopic constants of the bound states are determined. Our calculations confirm that the ground state of AlO+ cation is the X1Σ+ state. The permanent dipole moments (PDMs) functions of the selected bound states are computed. The spin–orbit (SO) matrix elements between the electronic states involved in the crossing region of the PECs are calculated to analyze the predissociation mechanisms of the X1Σ+, A1Π, and 21Σ+ states. Finally, the transition properties of four spin-allowed transitions are predicted, including the transition dipole moments (TDMs), Franck-Condon Factors (FCFs), and the radiative lifetimes. This work should enhance our understanding on the electronic structure and spectroscopy of AlO+ cation.

Multireference configuration interaction study of the 21 low-lying states of the OF radical

This paper calculated the potential energy curves of 21Λ-S and 42Ω states of the OF radical. The 21Λ-S states were the X2Π, A2Σ−, B2Σ−, C2Δ, D2Σ+, E2Σ+, 22Π, a4Σ−, b4Δ, 24Σ−, 14Σ+, 14Π, 24Π, 32Σ+, 32Σ−, 32Π, 42Π, 52Π, 22Δ, 32Δ, and 12Φ, which arose from the first two dissociation limits. The 42Ω states were generated from these Λ-S states. All the potential energy curves were calculated with the CASSCF method, which was followed by the icMRCI+Q approach. The 14Π, 24Π, 22Π, 42Π, 52Π, 32Σ+, and 32Δ states were repulsive whether the spin-orbit coupling effect included or not, but the A2Σ−, D2Σ+, 32Σ−, 22Δ, and 12Φ states became repulsive with the spin-orbit coupling effect included. Only the 16Ω states were bound. With the spin-orbit coupling effect accounted for, the X2Π state was inverted among the bound states; the X2Π, a4Σ−, and E2Σ+ states were strongly bound; and the 32Π, b4Δ, B2Σ−, C2Δ, 24Σ−, and 14Σ+ states were very weakly bound. The spectroscopic and vibrational properties were determined. Franck–Condon factors of some transitions were evaluated. The spin-orbit coupling effect on the spectroscopic parameters and vibrational properties was discussed. It is very difficult to explore the X2Π, a4Σ−, and E2Σ+ states by observing the electronic transitions between them because all these strong transitions originating only from the highly-vibrational states of the X2Π or a4Σ− state. It is also very hard to detect the 32Π, b4Δ, B2Σ−, C2Δ, 24Σ−, and 14Σ+ states by observing the transitions originating from these states, because these states are very weakly bound and unstable, though some transitions originating from them are very strong. These results can well explain why the OF radical is very difficult to detect in a spectroscopic experiment by observing the electronic transitions between different states.

Multireference configuration interaction study of ground and low-lying excited states of BrO radical

This work explored the spectroscopic parameters and vibrational properties of 12 states of BrO radical. The 12 states were X2Π, A2Π, 12Δ, 12Σ+, 12Σ−, 22Σ−, a4Σ−, 24Σ−, 14Σ+, 14Δ, 14Π, and 24Π, which were generated from the first dissociation limit, Br(2Pu)+O(3Pg). The potential energy curves were calculated with the CASSCF method, which was followed by the icMRCI approach with Davidson correction. Of the 12 electronic states, the 24Π state was repulsive. Each state had the single well and only the A2Π state had one barrier. The 12Δ, 12Σ+, 12Σ−, 22Σ−, 24Σ−, 14Σ+, 14Δ and 14Π states had only several vibrational levels and were very weakly-bound states, which well depths were less than 110cm−1. To improve the quality of potential energy curves, core-valence correlation and scalar relativistic corrections as well as the extrapolation to the complete basis set limit were included. The spectroscopic parameters and vibrational properties were determined. The transition dipole moments between two electronic states and Franck-Condon factors of some transitions were evaluated. The spin-orbit coupling effect on the spectroscopic parameters of the X2Π and A2Π states was discussed. The spectroscopic parameters and vibrational properties reported in this paper can be expected to be reliably predicted ones.

The low-lying doublet electronic excited states of TiO2−: A symmetry adapted cluster–configuration interaction (SAC-CI) study

The low-lying doublet excited states of the singly charged TiO2 anion (TiO2−) were investigated by the SAC-CI method. The vertical excitation spectrum of TiO2− was calculated at the SAC-CI/aug-cc-pVTZ levels. The ground electronic state (X2A1) and the lowest two valence excited states (22A1 and 12B1) having bound characters were optimized to stable C2v structures. A dipole-bound state (2A1) was found and optimized to a C2v structure. The adiabatic energies of the 22A1, 12B1, and dipole-bound states were obtained.