The calculation of atomic oscillator strengths: the lithium atom revisited

1992 ◽  
Vol 70 (2) ◽  
pp. 456-463 ◽  
Author(s):  
A. W. Weiss
Keyword(s):  
Oscillator Strength ◽  
Excited States ◽  
Configuration Interaction ◽  
Lithium Atom ◽  
Laser Excitation ◽  
Oscillator Strengths ◽  
Excitation Energies ◽  
Accurate Evaluation ◽  
Theoretical Predictions ◽  
Configuration Interaction Calculations

Extensive configuration interaction calculations have been done for the ground and first excited states of neutral lithium and singly ionized beryllium. While the calculations reproduce the ionization and excitation energies to within 3 cm−1 for Li and 10 cm−1 for Be+, the main purpose of this work is the accurate evaluation of the 2s–2p resonance line oscillator strength. The calculated value of 0.7478 agrees to within less than 1% with the very accurate laser excitation lifetime measurement of 0.7416 ± 0.0012. However, internal consistency checks of the accuracy of these calculations suggest that more precise calculations are unlikely to reduce this discrepancy significantly. Furthermore, when placed together with other independent calculations that should be of comparable, if not better, accuracy, all theoretical predictions strongly indicate an f-value of 0.7475 ± 0.0010, which differs from the experiment by 4 experimental standard deviations. Keywords: configuration interaction, correlation, oscillator strength.

Modification of HAM/3 excitation energies for ΠΠ* transitions of linear molecules

1980 ◽  
Vol 58 (16) ◽  
pp. 1687-1690 ◽  
Author(s):  
Delano P. Chong
Keyword(s):  
Excitation Energy ◽  
Explicit Expression ◽  
Excited States ◽  
Configuration Interaction ◽  
Excitation Energies ◽  
Carbon Suboxide ◽  
Numerical Examples ◽  
Energy Correction ◽  
Linear Molecules ◽  
Configuration Interaction Calculations

The excitation energies calculated by the HAM/3 procedure for ΠΠ* transitions in linear molecules can be internally inconsistent by as much as ± 0.6 eV. In the recent study by Åsbrink etal., the problem was avoided by adopting Recknagel's expressions and requiring the proper average ΠΠ* excitation energy. In this paper, we trace the small inconsistency back to its origin in HAM/3 theory and derive the analytical expression for the energy correction as well as Recknagel's formulas. Numerical examples studied include all seven linear molecules investigated by Åsbrink etal. The explicit expression for the correction enables us to perform meaningful configuration-interaction calculations on the excited states, as illustrated by the carbon suboxide molecule.

Ab initio MRD-CI Study of the Electronic Spectrum of Tribromomethanol Br3COH and the Photofragmentation along Br–C and C–O Cleavage

2003 ◽  
Vol 217 (3) ◽  
pp. 241-254
Author(s):  
M. Mühlhäuser
Keyword(s):  
Energy Range ◽  
Ab Initio ◽  
Electronic Spectrum ◽  
Oscillator Strength ◽  
Excited States ◽  
Atmospheric Chemistry ◽  
Configuration Interaction ◽  
Reference Configuration ◽  
Triplet States ◽  
Configuration Interaction Calculations

AbstractMulti reference configuration interaction calculations are carried out to compute the electronic spectrum of tribromomethanol Br3COH. The first dipole-allowed transitions are computed at 5.0 eV (11A″ ← X1A′) and 5.4 eV (21A″ ← X1A′) followed by three transitions at 5.5 eV (21A′ ← X1A′) and 6.1 eV (31A′ ← X1A′, 31A″ ← X1A′). The largest oscillator strength (f = 0.08) is obtained for the σ → σ* type excitation 31A″ ← X1A′ computed around 6.1 eV. The corresponding triplet states are also given. Five low-lying excited states in the energy range between 4.5 eV and 5.5 eV are found to be highly repulsive for Br–C elongation, leading to Br2CHOH (X2A′) and Br (X2P), so that tribromomethanol Br3COH is expected to be important for atmospheric chemistry as reservoir of Br radicals. Photodissociation along C–O cleavage resulting in Br3C (X2A′) and OH (X2Π) has to overcome a barrier of about 0.7 eV because the low-lying excited states 11A″, 13A′ and 13A″ become repulsive only after elongating the C–O bond by about 0.45 Å.

Theoretical studies on ClOO — electronic spectra, ionization potential, and electron affinity

2011 ◽  
Vol 89 (8) ◽  
pp. 891-897 ◽  
Author(s):  
Friedrich Grein
Keyword(s):  
Excited States ◽  
Ground State ◽  
Density Functional ◽  
Oscillator Strengths ◽  
Electron Affinities ◽  
Excitation Energies ◽  
Vertical Excitation ◽  
Avoided Crossings ◽  
Cluster Methods ◽  
Configuration Interaction Calculations

Vertical excitation energies and oscillator strengths of doublet and quartet states of ClOO, covering doublet states up to 7.5 eV and quartet states up to 9 eV, were obtained by multireference configuration interaction calculations. Strong absorptions from the X2A″ ground state are predicted at 186 and 235 nm. Experimentally, a maximum has been found near 248 nm. The grouping of excited states, with twelve low-lying doublet states and three low-lying quartet states, is explained by the interaction of the 2P ground state of Cl with the π*2 states 3Σg–, 1Δg, and 1Σg+ of O2. Potential energy curves for Cl–O separation at fixed O–O distance and ClOO angle show the lower states to be repulsive (with the exception of the ground state), and higher states to have minima due to avoided crossings. The lowest Rydberg states are expected around 8.5 eV. Adiabatic ionization potentials (IP) and electron affinities (EA) of ClOO were obtained by density functional and coupled cluster methods, with values of 11.60–11.79 eV for IP and 3.56–3.79 eV for EA.

The Importance of Photodissociative Trichloromethanol for Atmospheric Chemistry

2003 ◽  
Vol 68 (12) ◽  
pp. 2297-2308 ◽  
Author(s):  
Max Mühlhäuser ◽  
Melanie Schnell ◽  
Sigrid D. Peyerimhoff
Keyword(s):  
Energy Range ◽  
Excited States ◽  
Atmospheric Chemistry ◽  
Configuration Interaction ◽  
Configuration Interaction Calculations

Multireference configuration interaction calculations are carried out for ground and excited states of trichloromethanol to investigate two important photofragmentation processes relevant to atmospheric chemistry. For CCl3OH five low-lying excited states in the energy range between 6.1 and 7.1 eV are found to be highly repulsive for C-Cl elongation leading to Cl2COH (X2A') and Cl (X2P). Photodissociation along C-O cleavage resulting in Cl3C (X2A') and OH (X2Π) has to overcome a barrier of about 0.8 eV (13A'', 11A'') and 1.2 eV (13A') because the low-lying excited states 11A'', 13A' and 13A'' become repulsive only after elongating the C-O bond by about 0.3 Å.

scholarly journals Low-Cost Molecular Excited States from a State-Averaged Resonating Hartree-Fock Approach

2019 ◽  
Author(s):  
Jacob Nite ◽  
Carlos A. Jimenez-Hoyos
Keyword(s):  
Excited States ◽  
Configuration Interaction ◽  
Low Cost ◽  
Computational Cost ◽  
Mean Field ◽  
Chem Phys ◽  
Spin Projection ◽  
Excitation Energies ◽  
Hartree Fock ◽  
Orbital Relaxation

Quantum chemistry methods that describe excited states on the same footing as the ground state are generally scarce. In previous work, Gill et al. (J. Phys. Chem. A 112, 13164 (2008)) and later Sundstrom and Head-Gordon (J. Chem. Phys. 140, 114103 (2014)) considered excited states resulting from a non-orthogonal configuration interaction (NOCI) on stationary solutions of the Hartree–Fock equations. We build upon those contributions and present the state-averaged resonating Hartree–Fock (sa-ResHF) method, which differs from NOCI in that spin-projection and orbital relaxation effects are incorporated from the onset. Our results in a set of small molecules (alanine, formaldehyde, acetaldehyde, acetone, formamide, and ethylene) suggest that sa-ResHF excitation energies are a notable improvement over configuration interaction singles (CIS), at a mean-field computational cost. The orbital relaxation in sa-ResHF, in the presence of a spin-projection operator, generally results in excitation energies that are closer to the experimental values than the corresponding NOCI ones.

scholarly journals Low-Cost Molecular Excited States from a State-Averaged Resonating Hartree-Fock Approach

2019 ◽  
Author(s):  
Jacob Nite ◽  
Carlos A. Jimenez-Hoyos
Keyword(s):  
Excited States ◽  
Configuration Interaction ◽  
Low Cost ◽  
Computational Cost ◽  
Mean Field ◽  
Chem Phys ◽  
Spin Projection ◽  
Excitation Energies ◽  
Hartree Fock ◽  
Orbital Relaxation

Quantum chemistry methods that describe excited states on the same footing as the ground state are generally scarce. In previous work, Gill et al. (J. Phys. Chem. A 112, 13164 (2008)) and later Sundstrom and Head-Gordon (J. Chem. Phys. 140, 114103 (2014)) considered excited states resulting from a non-orthogonal configuration interaction (NOCI) on stationary solutions of the Hartree–Fock equations. We build upon those contributions and present the state-averaged resonating Hartree–Fock (sa-ResHF) method, which differs from NOCI in that spin-projection and orbital relaxation effects are incorporated from the onset. Our results in a set of small molecules (alanine, formaldehyde, acetaldehyde, acetone, formamide, and ethylene) suggest that sa-ResHF excitation energies are a notable improvement over configuration interaction singles (CIS), at a mean-field computational cost. The orbital relaxation in sa-ResHF, in the presence of a spin-projection operator, generally results in excitation energies that are closer to the experimental values than the corresponding NOCI ones.

Excitation energies in Be: A comparison of multiconfigurational linear response and full configuration interaction calculations

1986 ◽  
Vol 85 (11) ◽  
pp. 6544-6549 ◽  
Author(s):  
Richard L. Graham ◽  
Danny L. Yeager ◽  
Jeppe Olsen ◽  
Poul Jo/rgensen ◽  
Robert Harrison ◽  
...  
Keyword(s):  
Configuration Interaction ◽  
Linear Response ◽  
Excitation Energies ◽  
Full Configuration Interaction ◽  
Configuration Interaction Calculations

The ground state and low-lying excited states of CCCN radical and its ions: a CASSCF/CASPT2 study

2016 ◽  
Vol 94 (9) ◽  
pp. 803-807
Author(s):  
Angyang Yu
Keyword(s):  
Excited States ◽  
Ground State ◽  
Linear Structure ◽  
Electronic Configuration ◽  
Geometric Optimization ◽  
Oscillator Strengths ◽  
Basis Set ◽  
Excitation Energies ◽  
Complete Active Space ◽  
Vertical Excitation

The ground state and low-lying excited states of the CCCN radical and its ions have been investigated systematically using the complete active space self-consistent field (CASSCF) and multi-configuration second-order perturbation theory (CASPT2) methods in conjunction with the ANO-RCC-TZP basis set. The calculated results show that the state 12Σ+ has the lowest CASPT2 energy among the electronic states. By means of the geometric optimization of this radical, it could be found that the molecule exhibits linear structure, with the bond lengths R1 = 1.214 Å, R2 = 1.363 Å, R3 = 1.162 Å, which are very close to the experimental values. The calculated vertical excitation energies and the corresponding oscillator strengths show that there are three relatively strong peaks at energies 0.63, 4.04, and 5.49 eV, which correspond to the transitions 12Σ+ → 12Π, 12Σ+ → 22Π, and 12Σ+ → 22Σ+, respectively. Additionally, the electronic configuration and the harmonic vibration frequencies of each state are also investigated.

Accurate study on the properties of spectral lines for Na-like Cr13+

2019 ◽  
Vol 97 (4) ◽  
pp. 436-442
Author(s):  
A.K. Singh ◽  
Mayank Dimri ◽  
Dishu Dawra ◽  
Alok K.S. Jha ◽  
Man Mohan
Keyword(s):  
Configuration Interaction ◽  
Energy Levels ◽  
Electric Quadrupole ◽  
General Purpose ◽  
Spectral Lines ◽  
Oscillator Strengths ◽  
Fusion Plasma ◽  
Configuration Interaction Method ◽  
Magnetic Quadrupole ◽  
Configuration Interaction Calculations

An extended calculation of energy levels, radiative rates, and lifetimes are reported for sodium-like chromium. Extensive configuration interaction calculations have been performed using general-purpose relativistic atomic structure package (GRASP). The radiative rates, oscillator strengths, and line strengths are listed for all electric dipole (E1) transitions. However, for magnetic dipole (M1), electric quadrupole (E2), and magnetic quadrupole (M2) transitions, only radiative rates are listed. The importance of valence–valence (VV) and core–valence (CV) correlation effects in the calculation of energy levels have also been shown. To confirm the accuracy of the present results for energy levels by GRASP, independent calculations have been performed by using Flexible Atomic Code (FAC) and configuration interaction method (CIV3). The accuracy of the present levels, wavelengths, transition rates, and lifetimes are assessed by comparing them to available experimental and other theoretical results. We believe that our extensive results may be beneficial in fusion plasma research and astrophysical investigations and applications.

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