Generalized relativistic effective core potential calculations of the adiabatic potential curve and spectroscopic constants for the ground electronic state of the Ca 2 molecule (original) (raw)
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A bstract. T he di ssoci ati on energy, equi l i bri um di stance, and spectroscopi c constantsforthe 1 + g ground state ofthe Y b 2 m ol ecul e are cal cul ated.T he rel ati vi sti c e ectsarei ntroduced through general i zed rel ati vi sti ce ecti vecorepotenti al sw i th very hi gh preci si on. T he scal ar rel ati vi sti c coupl ed cl uster m ethod parti cul arl y wel lsui ted forcl osed-shel lvan-der-W aal ssystem si sused forthe correl ati on treatm ent.Extensi ve general i zed correl ati on basi ssetswere constructed and em pl oyed.T he rel ati vel y sm al l correcti onsforhi gh-ordercl usteram pl i tudesand spi n-orbi ti nteracti onsare taken i nto accountusi ng sm al l er basi s sets and the spi n-orbi t densi ty functi onaltheory.
The Journal of Physical Chemistry A, 2011
A set of benchmark results for the geometries, binding energies, and protonation affinities of 24 complexes of small organic ligands with Ca(II) is provided. The chosen level of theory is CCSD(T)/CBS obtained by means of a composite procedure. The performance of four density functionals, namely, PW91, PBE, B3LYP, and TPSS and several Pople-type basis sets, namely, 6-31G(d), 6-31+G(d), 6-31+G(2d,p) and 6-311+G(d) have been assessed. Additionally, the nature of the metal ligand bonding has been analyzed by means of the Symmetry Adapted Perturbation Theory (SAPT). We have found that the B3LYP hybrid functional, in conjunction with either the polarized double-ζ 6-31+G(2d,p) or the triple-ζ 6-311+ G(d) basis sets, yields the closest results compared to the benchmark data. The SAPT analysis stresses the importance of induction effects in the binding of these complexes and suggests that consideration of classical electrostatic contributions alone may not be reliable enough for the prediction of relative binding energies for Ca(II) complexes.
Theoretical study of the atomic spectra of the calcium atom
Chemical Physics Letters, 1992
Theoretical calculations are reported for the following terms of the atomic spectra of the Ca atom: ~ S (4s 2 ), l p (4s4p), 3p (4s4p), ~D(4s3d), 3D(4s3d), ~P(4s5p), 3p(4s5p). The method is based on all-electron calculations at the Hartree-Fock level followed by a configuration interaction for the two valence electrons. Core-valence (or intershell) correlation effects are introduced via a second-order perturbation development or via a core-polarization potential. The agreement with the experimental spectra is very good.
Accurate calculations of spectroscopic constants for the Yb dimer
The dissociation energy, equilibrium distance, and vibrational constant for the ground state of the Yb2 molecule are calculated. The relativistic effects are introduced through generalized relativistic effective core potentials with very high precision. The scalar relativistic coupled cluster method particularly well suited for closed-shell van-der-Waals systems is used for the correlation treatment. Extensive generalized correlation basis sets were constructed and employed. The corrections for high-order cluster amplitudes and spin-orbit interactions are taken into account.
An ab initio study of the lowest electronic states of yttrium dicarbide, YC[sub 2]
The Journal of Chemical Physics, 2005
The low-lying electronic states of yttrium dicarbide have been calculated using highly correlated wave functions and systematic sequences of correlation consistent basis sets. For the 2 A 1 ground electronic state, the near-equilibrium potential energy surface ͑PES͒ has been calculated using the coupled cluster method in conjunction with basis sets ranging in size from double to quintuple . The relativistic effects have been taken into account by using pseudopotentials for the Y atom. After extrapolation to the complete basis set limit, additional corrections due to core-valence correlation and spin-orbit effects have also been included. The same approach has been followed for the 2 B 1 , 2 B 2 , and 2 A 2 states but only the C 2V PESs have been considered in these cases. For the two 2 A 1 electronic excited states and, for comparison purposes, for the ground state, the multireference configuration interaction ͑MRCI͒ approach has been used in conjunction with double-and triplebasis sets for the construction of the PES. The molecular and spectroscopic properties predicted for the ground and excited states investigated in this work compare well with the available experimental data, particularly for the ground electronic state. The 0 K dissociation enthalpy of YC 2 , ⌬H Y-C 2 ͑0 K͒, and its atomization enthalpy, ⌺D 0 , are predicted to be 148.4 and 291.5 kcal/ mol, respectively.
Effective Hamiltonian parameters forab initioenergy-level calculations of SrCl2:Yb2+and CsCaBr3:Yb2+
Journal of Physics: Condensed Matter, 2013
Calculated energy levels from recent ab initio studies of the electronic structure of SrCl 2 :Yb 2+ and CsCaBr 3 :Yb 2+ are fitted with a semi-empirical "crystal-field" Hamiltonian, which acts within the model space 4f 14 +4f 13 5d+4f 13 6s. Parameters are obtained for the minima of the potential-energy curves for each energy level and also for a range of anion-cation separations. The parameters are compared with published parameters fitted to experimental data and to atomic calculations. The states with significant 4f 13 6s character give a good approximation to the impurity-trapped exciton states that appear in the ab initio calculations.
Physical Review A, 1999
Excitation energies and oscillator strengths of neutral calcium ͑Ca I͒ are calculated through third order using a variant of the multireference many-body perturbation theory, known as the effective valence-shell Hamiltonian (H v) method. Transition energies, oscillator strengths, and binding energies of various states are computed and compared with experimental and other theoretical data. These quantities are in favorable agreement with the experiment and other correlated calculations. The basis and valence space dependence of the H v scheme are addressed with some illustrative examples. ͓S1050-2947͑99͒06905-X͔