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Third-Order Unitary Coupled Cluster (UCC3) for Excited Electronic States: Efficient Implementation and Benchmarking
摘要： The efficient implementation of the third-order unitary coupled-cluster scheme (UCC3) for the calculation of excited electronic states is reported. The UCC3 scheme and its second-order UCC2 variant have been benchmarked and compared to Jacquemin’s recently introduced as well as Thiel’s well-established benchmark sets for excitation energies and oscillator strengths. For the latter, the calculation of 134 excited singlet and 71 excited triplet states of 28 small to medium-sized organic molecules has revealed that UCC2 exhibits a mean error and standard deviation of 0.36 ± 0.41 eV for singlet states and 0.22 ± 0.21 eV for triplet states, whereas UCC3 revealed an accuracy of 0.06 ± 0.27 eV for singlet and ?0.22 ± 0.15 eV for triplet states. Additionally, the oscillator strengths obtained with effective transition moments correct through second order in perturbation theory are in very good agreement with literature data.
关键词： perturbation theory,unitary coupled-cluster,oscillator strengths,excited electronic states,benchmarking
更新于2025-09-23 15:21:01
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Variation of the oscillator strengths for the <i>α</i> emission lines of the one- and two-electrons ions in dense plasma
摘要： We present the results of a detailed theoretical study on the variation of the oscillator strengths for the 1s ! 2p transition of the H-like ions and the 1s2 1S ! 1s2p 1P transition of the He-like ions (or, inversely, the Lyman-a and Hea emission lines, respectively) subject to external plasma which meet the spatial and temporal criteria of the Debye-H€uckel (DH) approximation. Our study shows that the resulting oscillator strength decreases for the Hea line for He-like ions, similar to the Lyman-a emission lines for all H-like ions, as the effect of the external plasma increases with the decreasing Debye length D in terms of a reduced Debye length kD ? Zeff D. A nearly universal feature is demonstrated for a scaled oscillator strength as a function of the reduced Debye length kD ? (Z (cid:2) 1)D for different He-like ions that meet the same criteria for the DH model. The percentage changes of the oscillator strengths from their plasma-free values are substantially greater than those for the corresponding change for the redshifts of the Lyman-a and Hea emission lines subject to outside dense plasma. Should these general features be demonstrated experimentally, the theoretical procedure presented in this study could easily be applied to extrapolate from a single calculation for one He-like ion to other He-like ions, which could offer an alternative to complement other diagnostic efforts of the dense plasma.
关键词： He-like ions,oscillator strengths,dense plasma,Debye-H€uckel approximation,H-like ions
更新于2025-09-23 15:21:01
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Luminescence properties of Nd3+ ions doped P2O5-Li2O3-GdF3 glasses for laser applications
摘要： The phosphate glass doped with Nd3+ ions, is a recognized high gain laser material due to better spectroscopic properties. In present study, the luminescent properties of Nd3+ doped lithium-gadolinium phosphate glasses were investigated. The compactness of the glass matrix believed to increase with increasing concentration of Nd2O3 contents, because the density of the samples also increases in same fashion. Furthermore, the emission spectra monitor after 804 nm excitation show three emission peaks at 874, 1065 and 1333 nm. In the present work maximum emission intensity recorded for 1 mol% of Nd2O3 and above 1 mol% the emission intensity decrease. The Judd-Ofelt (JO) theory applied to calculate the JO intensity parameters (Ω2, 4, 6), oscillator strength for absorption spectra, several radiative properties for the prepared glasses. The calculated JO intensity parameters show the Ω4 > Ω6 > Ω2 trend which indicate rigid nature of the present glasses. The radiative transition probability, stimulated emission cross section and branching ratio show higher values for 4F3/2→4I11/2 transition. From properties evaluated in the present work it is concluded that the glass doped with 1.0 mol% Nd2O3 can be a potential candidate for laser applications.
关键词： Oscillator strengths,Branching ratio,Luminescent properties,JO theory
更新于2025-09-16 10:30:52
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) formation: Comparison with
摘要： Superexcited states of H2S have been investigated with determining the cross sections for emission of dispersed and nondispersed atomic ?uorescence against the incident photon energy in the range 11–40 eV to address the ionization and excitation of the valence electrons. This method enables us to extract the discrete electronic state from the superposition with continuous electronic states. The cross sections for H(2p) formation have been put on an absolute scale. Ten superexcited states have been found, two in the range 13–15 eV are singly excited 2b?1 2 (mo) states with a single con?guration and the other eight states in the range 16–25 eV are doubly excited states with multiple con?gurations. State-resolved dipole oscillator strengths for H(2p) formation in the photoexcitation of H2S have been determined. Similar experiments have been performed for H2O. The state-resolved dipole oscillator strengths for H(2p) formation in the photoexcitation of H2S are ～10?3, whereas those in the photoexcitation of H2O range from ～10?3 to ～10?2. It is found that major fragment atoms are H(2p) atoms in the photoexcitation of H2O and S? in the photoexcitation of H2S. The superexcited states of H2O and H2S are compared based on the similarity and difference of the electronic structures. It turns out from the comparison that (i) the smaller values of the dipole oscillator strengths for H(2p) formation in the photoexcitation of H2S are related to the change of the major fragment atoms and (ii) the energy splitting of the doubly excited “4a?1 1 (mo(cid:4))” states of H2O. This enhancement is caused by the stronger electron correlation in H2S than in H2O. The similarity in shape is indicated between the inner valence band and inner shell band in the ?uorescence cross sections against the incident photon energy for H2S and H2O.
关键词： superexcited states,H2O,dipole oscillator strengths,electron correlation,H2S,double photoexcitation
更新于2025-09-09 09:28:46
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) method
摘要： Absolute optical oscillator strengths of the Lyman and Werner bands of molecular deuterium are determined by a dipole(γ , γ ) method with the high energy resolution of 25 meV. A comprehensive comparison shows that an excellent agreement between the present experimental results and the earlier theoretical calculations is achieved for both Lyman and Werner bands. In addition, the electronic transition dipole moments of D2 are derived. The absolute optical oscillator strengths of the Lyman and Werner bands of D2 reported in this work can serve as the benchmark to test calculations with different theoretical models and calculational codes and, also, be used in thermonuclear fusion plasma and other ?elds.
关键词： γ ) method,dipole (γ,electronic transition dipole moments,molecular deuterium,Lyman and Werner bands,optical oscillator strengths
更新于2025-09-09 09:28:46