Search results for "Figuration"
showing 10 items of 615 documents
Full Configuration-Interaction Study on the Tetrahedral Li4 Cluster
2008
International audience; The Li4 cluster low lying electronic states were studied. In particular we investigated the tetrahedral geometry at full CI and coupled cluster level, with basis sets of increasing quality. The 5A2 electronic state, characterized by having all the valence electrons unpaired, forming a quite stable no-pair bonding state, was studied in greater detail. In order to compare the energies we also studied the Li4 rhombus singlet ground state. The ability of coupled cluster with perturbative triples to correctly reproduce energy levels in a quasi-degenerate system was validated with respect to the full CI.
Cost-Effective Treatment of Scalar Relativistic Effects for Multireference Systems: A CASSCF Implementation Based on the Spin-free Dirac-Coulomb Hami…
2016
We present an implementation of the complete active space-self-consistent field (CASSCF) method specifically designed to be used in four-component scalar relativistic calculations based on the spin-free Dirac-Coulomb (SFDC) Hamiltonian. Our implementation takes full advantage of the properties of the SFDC Hamiltonian that allow us to use real algebra and to exploit point-group and spin symmetry to their full extent while including in a rigorous way scalar relativistic effects in the treatment. The SFDC-CASSCF treatment is more expensive than its non-relativistic counterpart only in the orbital optimization step, while exhibiting the same computational cost for the rate-determining full conf…
Atomic structure calculations of superheavy noble element oganesson (Z=118)
2018
We calculate the spectrum and allowed E1 transitions of the superheavy element Og (Z=118). A combination of configuration interaction (CI) and perturbation theory (PT) is used (Dzuba \textit{et at.} Phys. Rev. A, \textbf{95}, 012503 (2017)). The spectrum of lighter analog Rn I is also calculated and compared to experiment with good agreement.
Prediction of quantum many-body chaos in protactinium atom
2017
Energy level spectrum of protactinium atom (Pa, Z=91) is simulated with a CI calculation. Levels belonging to the separate manifolds of a given total angular momentum and parity $J^\pi$ exhibit distinct properties of many-body quantum chaos. Moreover, an extremely strong enhancement of small perturbations takes place. As an example, effective three-electron interaction is investigated and found to play a significant role in the system. Chaotic properties of the eigenstates allow one to develop a statistical theory and predict probabilities of different processes in chaotic systems.
Theoretical study of the electron structure of superheavy elements with an open 6d shell: Sg, Bh, Hs, and Mt
2019
We use recently developed efficient versions of the configuration interaction method to perform {\em ab initio} calculations of the spectra of superheavy elements seaborgium (Sg, $Z=106$), bohrium (Bh, $Z=107$), hassium (Hs, $Z=108$) and meitnerium (Mt, $Z=109$). We calculate energy levels, ionization potentials, isotope shifts and electric dipole transition amplitudes. Comparison with lighter analogs reveals significant differences caused by strong relativistic effects in superheavy elements. Very large spin-orbit interaction distinguishes subshells containing orbitals with a definite total electron angular momentum $j$. This effect replaces Hund's rule holding for lighter elements.
Using optical clock transitions in Cu II and Yb III for time-keeping and search for new physics
2021
We study the $^1$S$_0 - ^3$D$_2$ and $^1$S$_0 - ^3$D$_3$ transitions in Cu II and the $^1$S$_0 - ^3$P$^{\rm o}_2$ transition in Yb III as possible candidates for the optical clock transitions. A recently developed version of the configuration (CI) method, designed for a large number of electrons above closed-shell core, is used to carry out the calculation. We calculate excitation energies, transition rates, lifetimes, scalar static polarizabilities of the ground and clock states, and blackbody radiation shift. We demonstrate that the considered transitions have all features of the clock transition leading to prospects of highly accurate measurements. Search for new physics, such as time va…
Nobelium energy levels and hyperfine structure constants
2018
Advances in laser spectroscopy of superheavy ($Z>100$) elements enabled determination of the nuclear moments of the heaviest nuclei, which requires high-precision atomic calculations of the relevant hyperfine structure (HFS) constants. Here, we calculated the HFS constants and energy levels for a number of nobelium (Z=102) states using the hybrid approach, combining linearized coupled-cluster and configuration interaction methods. We also carried out an extensive study of the No energies using 16-electron configuration interaction method to determine the position of the (5f^{13}7s^2 6d) and (5f^{13}7s^2 7p) levels with a hole in the 5f shell to evaluate their potential effect on the hype…
Pressure dependence of the exciton absorption and the electronic subband structure of aGa0.47In0.53As/Al0.48In0.52As multiple-quantum-well system
1992
We have measured the optical absorption of a ${\mathrm{Ga}}_{0.47}$${\mathrm{In}}_{0.53}$As/${\mathrm{Al}}_{0.48}$${\mathrm{In}}_{0.52}$As multiple quantum well at 10 K for pressures up to 7 GPa. The energies of optical transitions between heavy- and light-hole subbands and electron levels of the wells show a blueshift with pressure similar to the bulk lowest direct band gap. We observe a decrease with pressure of the energy splitting between heavy- and light-hole subbands with the same quantum number n. From the analysis of the absorption line shape, we have obtained the pressure dependences of exciton binding energies, oscillator strengths, and linewidths. These results are interpreted in…
Ground and Excited State First-Order Properties in Many-Body Expanded Full Configuration Interaction Theory
2020
The recently proposed many-body expanded full configuration interaction (MBE-FCI) method is extended to excited states and static first-order properties different from total, ground state correlation energies. Results are presented for excitation energies and (transition) dipole moments of two prototypical, heteronuclear diatomics---LiH and MgO---in augmented correlation consistent basis sets of up to quadruple-$\zeta$ quality. Given that MBE-FCI properties are evaluated without recourse to a sampled wave function and the storage of corresponding reduced density matrices, the memory overhead associated with the calculation of general first-order properties only scales with the dimension of …
Controlled type-I–type-II transition in GaAs/AlAs/AlxGa1−xAs double-barrier quantum wells
1997
We show that the insertion of extremely narrow AlAs layers in double-barrier GaAs/AlAs/${\mathrm{Al}}_{\mathrm{x}}$${\mathrm{Ga}}_{1\mathrm{\ensuremath{-}}\mathrm{x}}$As quantum wells results in a variety of electronic configurations, thus providing a powerful tool for tailoring the electronic transitions in GaAs heterostructures. In particular, the transition from type-I to type-II recombination is shown to occur in correspondence with variations by a single monolayer in the thickness of the AlAs and/or GaAs layers. Drastic changes in the recombination lifetimes are correspondingly observed; at the same time, the photoluminescence efficiency is found to be almost independent of the type-I-…