CI calculations for ground and the lowest core-excited states of Li and Li− (original) (raw)
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The Journal of Chemical Physics, 2007
Explicitly correlated Gaussian functions have been used to perform very accurate variational calculations for the ground states of 7 Li and 7 Li −. The nuclear motion has been explicitly included in the calculations ͑i.e., they have been done without assuming the Born-Oppenheimer ͑BO͒ approximation͒. An approach based on the analytical energy gradient calculated with respect to the Gaussian exponential parameters was employed. This led to a noticeable improvement of the previously determined variational upper bound to the nonrelativistic energy of Li −. The Li energy obtained in the calculations matches those of the most accurate results obtained with Hylleraas functions. The finite-mass ͑non-BO͒ wave functions were used to calculate the ␣ 2 relativistic corrections ͑␣ =1/c͒. With those corrections and the ␣ 3 and ␣ 4 corrections taken from Pachucki and Komasa ͓J. Chem. Phys. 125, 204304 ͑2006͔͒, the electron affinity ͑EA͒ of 7 Li was determined. It agrees very well with the most recent experimental EA.
Physical Review A, 2013
The total energies of twenty eight bound S-, P-, D-, F-, G-, Hand nd I-states in the three-electron Li atom and Be + ion, respectively, are determined with the use of the Configuration Interaction (CI) with Slater orbitals and L-S eigenfunctions, and the Hylleraas-configuration-interaction (Hy-CI) methods. We discuss the construction and selection of the configurations in the wave functions, optimization of the orbital exponents and advanced computational techniques. Finally, we have developed an effective procedure which allows one to determine the energies of the excited states in three-electron atoms and ions to high accuracy by using compact wave functions. For the ground and low lying excited states our best accuracy with the Hy-CI method was ≈ 1 • 10 −6 a.u. and 1 • 10 −4 a.u. for other excited states. Analogous accuracy of the CI method is substantially lower ≈ 1 • 10 −3 a.u. Many of the rotationally excited (bound) states in the three-electron Li atom and Be + ion have never been evaluated to such an accuracy.
Ground and excited states of Li−, Be− through a density-based approach
Chemical Physics Letters, 2007
Density functional calculations are performed for ground [He]2s 2 1 S e , and three metastable bound excited states, 1s2s2p 2 5 P e , 1s2p 3 5 S o , 1s2s2p3p 5 P e of Li − and [He]2s2p 2 4 P e , [He]2p 3 4 S o , 1s2s2p 3 6 S o of Be − each. The work-function-based exchange potential is used, while the correlation effects are included by employing the Lee-Yang-Parr potential. The relevant nonrelativistic KS equation is solved by means of a generalized pseudospectral discretization scheme offering nonuniform and optimal spatial grid. Computed total energies, radial densities, selected density moments, as well as two transition wavelengths (1s2s2p 2 5 P e →1s2p 3 5 S o of Li − , [He]2s2p 2 4 P e → [He]2p 3 4 S o of Be − ) show reasonably good agreement with the available theoretical and experimental data. The term energies show an absolute deviation of 0.007-0.171% with the largest deviation being observed for the even-parity 5 P state of Li − . The transition wavelengths of Li − , Be − are calculated within 0.891 and 0.438% of the experimental values. This offers a simple practical route towards accurate reliable calculation of excited states of anions within density functional theory.
Atomic configuration interaction and studies of He, Li, Be, and Ne ground states
Physical Review A, 1997
The atomic configuration interaction (CI) is reconsidered. We compare the algebraic and geometric approaches to the construction of the CI matrix and point out advantages of the latter. One-electron basis sets of quality comparable to numerical multiconfigurational Hartree-Fock are readily obtained. The generation of large CI lists of symmetry eigenfunctions is monitored by a prescription establishing an a priori identification of relevant contributions to the wave function. Systematic and well-defined truncations to multireference CI's are examined. A formula for energy contributions of six-excited unlinked clusters is derived and shown to give reasonable estimates. Ensuing nonrelativistic CI calculations on He, Li, Be, and Ne ground states yield the lowest upper bounds in the literature, capturing 99.978, 99.923, 99.919, and 99.59% of the accepted correlation energies, respectively.
Accurate calculations for the even-parity core-excitedP2states of neutral Li
Physical review, 1979
Nonrelativistic configuration-interaction calculations have been carried out with orbital basis specifically adapted for each one-of the first seven even-parity P bound states of neutral Li. The results show that the. lowest four 'P states have recently been observed by absorption spectroscopy from the 1s'2p state. The calculated transition wavelengths (20.7452, 19.7613, 19. 4728, and 19.4065+0.0005 nm agree well with the experimental ones (20.744, 19.762, 19.474, and 19.405+0.002 nm). Electric dipole transition probabilities to the 1s '2p, 3p and 4p states have also been calculated. The configurations for the two lowest 'P(1) and 'P(2) states are 1s2p and (ls2p)'P3p, respectively. The (1s2p)'P np and (1s2p)'P n'p series almost coincide at n = 4, n' = 3, and as a consequence, the 'P(3) and P(4) levels are approximately described by (1s2p)'P4p+(1s2p)'P3p. This is the simplest known example of two-level series which mutually perturb each other.
Calculations on theS2ground state of the lithium atom
Physical Review A, 1986
Extensive variational. calculations on the S ground state of the lithium atom are reported. %ith use of a 352-term Hylleraas-type expansion, the nonrelativistic ground-state energy of 5 Lit is determined to be-7.478058 a.u. , which lies approximately 3 cm above empirical estimates of the nonrelativistic ground-state energy. This variational upper bound to the ground-state energy is the lowest to our knowledge reported to date in the literature. A number of expectation values, including the individual energy terms, the Fermi-contact interaction, the electron density at the nucleus, and the moments (rP), n =1-3, and (r;J), n =1,2, are also evaluated. The general rates of convergence of the calculation are discussed. The role played by the two doublet spin eigenfunctions is examined, and the importance of including both of these functions for the accurate calculation of the Fermi-contact interaction is discussed.
The effects of coupling to the target continuum on the electron-impact excitation of Li
Journal of Physics B: Atomic, Molecular and Optical Physics, 2003
We have investigated the effects of coupling to the continuum and high bound states on the electron-impact excitation of He-like Li + using the R matrix with pseudostates (RMPS) method. Previous studies on this ion have focused on transitions from the ground state to the n = 2 terms. In this work, we have determined collision strengths between all 19 terms through n = 4. We present the results of two RMPS calculations with different numbers of pseudostates in order to study the convergence of the collision strengths with the size of the pseudostate expansion. In addition, we compare the RMPS collision strengths with the results of an R-matrix calculation without pseudostates in order to determine the influence of the continuum coupling as a function of electron energy. As one might expect, coupling to the target continuum has quite large effects on the collision strengths for excitation to the n = 3 and 4 terms at energies above the ionization limit. However, we find that these effects are also significant for excitation to the n = 2 terms and that they persist down to energies just above the excitation thresholds. The experience gained from this work will allow us to pursue similar studies in more complex target systems. Furthermore, the results of our largest RMPS calculation provide the most complete and accurate set of excitation data for this ion, which is of significant importance to research in controlled nuclear fusion.
Isoelectronic study of triply excited Li-like states
Journal of Physics B: Atomic, Molecular and Optical Physics, 2003
Absolute doubly differential cross sections (DDCSs) for the production and Auger decay of the intra-shell 2s2p 2 2 D triply excited state formed in collisions of He-like ions (Z = 5-9) with H 2 were determined experimentally, using zero-degree Auger projectile electron spectroscopy. The 2 D e state was directly produced by 180 • resonant scattering of the quasi-free H 2 electrons from the 1s2s 3 S metastable state of the ion. Resonant energies and DDCSs calculated using the R-matrix approach within the electron scattering model were found to be in good overall agreement with experiment.
Nonrelativistic energy of the Li ground state
Physical Review A, 1991
Configuration-interaction calculations with energy-optimized basis sets and an empirical estimate of all sources of truncation-energy errors are used to evaluate the nonrelativistic electronic energy of the Li ground state. Our result E", =-7.4780624(7) a.u. (Li) is 3 phartree below an upper bound recently obtained by King using Hylleraas-type calculations, and 11 phartree above an old estimate based on experimental data supplemented by relativistic, radiative, and mass-polarization corrections, thus suggesting a reassessment of several related issues.
A benchmark study of Li2+, Li2−, LiH+ and LiH−: Quantum Monte-Carlo and coupled-cluster computations
Computational and Theoretical Chemistry, 2017
For the first time, very accurate potential energy curves (PEC) have been computed by the all electron Diffusion Quantum Monte-Carlo (DMC) and CCSD(T) methods for the ground-state of the Li 2 + , Li 2-, LiH + and LiHions. In addition to the molecular moieties, Li + , Li-, Hions have also been studied by the aforementioned methods. The employed trial wave functions for the DMC calculations are a multiplication of multi-configuration expansions 2 which are prepared by the Complete Active Space Self-Consistent Field method (CASSCF) with the aug-cc-pVTZ and the aug-cc-pCVTZ basis sets and the Jastrow factor. The CCSD(T) computations with all electrons correlated, have been performed by the cc-pV5Z, aug-cc-pCVQZ and aug-cc-pV6Z basis sets. In addition, the correlation energies for all of the studied atomic and molecular species have been calculated. For the studied molecular species, the Hartree-Fock energies in the complete basis set limit (E CBS) have not been reported. In this work for each of the molecular systems, the most negative energy which has been computed by the cc-pV5Z or aug-cc-pCVQZ basis sets has been used. The obtained PECs by the DMC and CCSD(T) methods are used to calculate the vibration-rotation energy levels and spectroscopic constants.