M. Krośnicki

Valence ab initio calculation of the potential energy curves for the Sr2 dimer

The electronic structure of the Ca2 molecule has been investigated by use of a two-valence-electron semiempirical pseudopotential and applying the internally contracted multireference configuration interaction method with complete-active-space self-consistent-field reference wave functions. Core–valence correlation effects have been accounted for by adding a core-polarization potential to the Hamiltonian. The ground-state properties of the Ca2 and Ca2+ dimers have also been studied at the single-reference coupled-cluster level with single and double excitations including a perturbative treatment of triple excitations. Good agreement with experiment has been obtained for the ground-state potential curve and the only experimentally known A1Σu+ excited state of Ca2. The spectroscopic parameters De and Re deduced from the calculated potential curves for other states are also reported. In addition, spin–orbit coupling between the singlet and triplet molecular states correlating, respectively, with the (4p)1P and (4p)3P Ca terms has been investigated using a semi-empirical two-electron spin–orbit pseudopotential.

Valence ab initio calculation of the potential energy curves for Ca–rare gas van der Waals molecules

Abstract Adiabatic potential curves for the ground state and several low-lying excited states of the calcium atom interacting with rare gas (RG) atoms have been obtained in the ΛS coupling scheme from valence ab initio complete-active-space multiconfiguration self-consistent-field (CASSCF)/complete-active-space multireference second-order perturbation theory (CASPT2) calculations. In the calculations the Ca 2+ and RG 8+ atomic cores are represented by scalar-relativistic energy-consistent pseudopotentials. Core polarization and core-valence correlation have been accounted for by adding a core polarization potential (CPP) to the Hamiltonian. Moreover, the closed-shell single-reference coupled-cluster approach with single and double excitations including a perturbative treatment of triple excitations (CCSD(T)) has been used to obtain more accurate ground-state potential curves for the species. The transition dipole moments from the ground state to the excited 1 Σ and 1 Π states correlating with the (3d) 1 D and (4p) 1 P Ca terms have been evaluated as a function of R . Fine structure of the molecular terms has also been studied using a semi-empirical two-electron spin–orbit pseudopotential for the Ca atom.

Quasirelativistic valence ab initio calculation of the potential energy curves for the Hg–rare gas atom complexes

Abstract Results of large-scale valence ab initio calculations of potential energy curves for ground and several excited states of the Hg–rare gas (RG) van der Waals molecules are reported. In the calculations, the Hg20+ and RG8+ cores are simulated by energy-consistent pseudopotentials which also account for scalar-relativistic effects and spin–orbit (SO) interaction. Potential energies in the ΛS coupling scheme have been evaluated by means of ab initio complete-active-space multiconfiguration self-consistent field (CASSCF)/complete-active-space multireference second-order perturbation theory (CASPT2) calculations, while the SO matrix has been computed in a reduced CI space restricted to the CASSCF level. Finally, the Ω potential curves are obtained by diagonalization of the modified SO matrix (its diagonal elements before diagonalization substituted by the corresponding CASPT2 eigenenergies). The calculated potential curves, especially the derived spectroscopic parameters for the ground and several excited states of the Hg–RG species are presented and discussed in the context of available experimental data. The theoretical results exhibit very good agreement with experiment.

Quasirelativistic valence ab initio calculation of the potential curves for the Zn–rare gas van der Waals molecules

Abstract Results of large scale valence ab initio calculations of the potential curves for the ground and several low lying excited states of the Zn–rare gas (RG) van der Waals molecules are reported. In the calculations, the Zn20+ and RG8+ cores are replaced by energy-consistent pseudopotentials which also account for scalar-relativistic effects and spin–orbit (SO) interaction. Potential energies in the ΛS coupling scheme have been obtained by means of valence ab initio complete-active-space multiconfiguration self-consistent-field (CASSCF)/complete-active-space multireference second-order perturbation theory (CASPT2) calculations. On the other hand, the corresponding SO matrix has been calculated in a reduced CI space restricted to the CASSCF level. The final Ω potential curves are obtained by diagonalization of the modified SO matrix (its diagonal elements before diagonalization substituted by the corresponding CASPT2 eigenenergies). The calculated potential curves, and particularly the derived spectroscopic parameters De, Re and ωe for the ground and excited states of the Zn–RG complexes are discussed in the context of available experimental data. Quite reasonable agreement between the theoretical results and experimental data has been obtained for all Zn–RG pairs.

Interatomic potentials of metal dimers: probing agreement between experiment and advanced ab initio calculations for van der Waals dimer Cd2

Abstract A critical review of experimental studies and ab initio calculations of the low-lying ungerade excited and ground state interatomic potentials of Cd2 van der Waals dimer is presented. Consistency as well as discrepancies between experimental results and ab initio calculations are probed. In order to obtain better agreement with existing experimental data, fill in gaps in current knowledge and provide a unifying framework, advanced all-electron ab initio calculations were performed and simulations of the reported spectra were executed. From simulations of laser-induced fluorescence excitation and dispersed emission spectra, analytical and/or point-wise representations of the (51P1), B11u(51P1), a31u(53P1), (53P1) and c31u(53P2) excited-, and the (51S0) ground-state Cd2 interatomic potentials were obtained. The comparison of the ab initio calculated potentials with results of the analyses allows to illustrate a current state-of-the-art of theory-and-experiment correspondence for such a demanding system. Results are presented in the context of an importance of the group 2 and group 12 metal dimer interatomic potentials especially, in ultra-cold physics and chemistry, and in fundamental tests of quantum mechanics.