The question of bending of the alkaline earth dihalides MX2 (M = beryllium, magnesium, calcium, strontium, barium; X = fluorine, chlorine, bromine, iodine). An ab initio pseudopotential study

This work presents the development of first-principles bromide ion-water interaction potentials using the mobile charge density in harmonic oscillators-type model. This model allows for a flexible and polarizable character of the interacting molecules and has already been parametrized for waterwater interactions. The prospected potential energy surfaces of the bromide ion-water system were computed quantum-mechanically at Hartree-Fock and Møller-Plesset second-order perturbation levels. In addition to the ion-solvent molecule pair, structures formed by the anion and two or three water molecules were considered in order to include many body effects. Minimizations of hydrated bromide clusters in gas phase ͓Br( -6,10,15,20) and Monte Carlo computations of bromide aqueous solutions were performed to test the new potentials. Both structural and thermodynamic properties have been studied in detail and compared to the available experimental and theoretical values. From these comparisons, it was concluded the importance of including basis set superposition error corrections for the two-body interactions, and the small role of both electron correlation on the three-body terms and the four-body terms. Monte Carlo simulation results have also been used to investigate if the presence of the anion significantly affects the intramolecular geometry of the water molecules and the degree of disruption of the water solvent structure in its vicinity.

Section: B Quantum-mechanical Calculationsmentioning

confidence: 99%

Development of first-principles interaction model potentials. An application to the study of the bromide hydration

Ayala

Martı́nez

Pappalardo

et al. 2002

“…[30][31][32][33][34] An effective core pseudopotential ͑ECP͒ was used to describe the core electrons in the case of the iodide ion, namely, the SDB-ECP, 35 while the aug-cc-pVTZ basis sets augmented with polarization functions 36 were used for the valence electrons.…”

Section: Methodsmentioning

confidence: 99%

Study of the stabilization energies of halide-water clusters: An application of first-principles interaction potentials based on a polarizable and flexible model

Ayala¹,

Martı́nez²,

Pappalardo³

et al. 2004

The aim of this work is to compute the stabilization energy E stab (n) of ͓X(H 2 O) n ͔ Ϫ (XϵF, Br, and I for nϭ1 -60) clusters from Monte Carlo simulations using first-principles ab initio potentials. Stabilization energy of ͓X(H 2 O) n ͔ Ϫ clusters is defined as the difference between the vertical photodeachment energy of the cluster and the electron affinity of the isolated halide. On one hand, a study about the relation between cluster structure and the E stab (n) value, as well as the dependence of the latter with temperature is performed, on the other hand, a test on the reliability of our recently developed first-principles halide ion-water interaction potentials is carried out. Two different approximations were applied: ͑1͒ the Koopmans' theorem and ͑2͒ calculation of the difference between the interaction energy of ͓X(H 2 O) n ͔ Ϫ and ͓X(H 2 O) n ͔ clusters using the same ab initio interaction potentials. The developed methodology allows for using the same interaction potentials in the case of the ionic and neutral clusters with the proviso that the charge of the halide anion was switched off in the latter. That is, no specific parametrization of the interaction potentials to fit the magnitude under study was done. The good agreement between our predicted E stab (n) and experimental data allows us to validate the first-principles interaction potentials developed elsewhere and used in this study, and supports the fact that this magnitude is mainly determined by electrostatic factors, which can be described by our interaction potentials. No relation between the value of E stab (n) and the structure of clusters has been found. The diversity of E stab (n) values found for different clusters with similar interaction energy indicates the need for statistical information to properly estimate the stabilization energy of the halide anions. The effect of temperature in the prediction of the E stab (n) is not significant as long as it was high enough to avoid cluster trapping into local equilibrium configurations which guarantees an appropriate sampling of the configurational space. Parallel tempering method was applied in particular cases to guarantee satisfactory sampling of clusters at low temperature.

“…3 Klemperer and colleagues demonstrated the existence of nonzero dipole moments in electric deflection experiments. 4,5 There have since been numerous investigations concerning the factors governing the propensity for linear versus bent geometries.…”

Section: Introductionmentioning

confidence: 99%

“…4,5 There have since been numerous investigations concerning the factors governing the propensity for linear versus bent geometries. 3,[6][7][8] Polarization and d-hybridization appear to play important roles. The ''dimer'' species M 2 X 4 have been computed to have many isomers, generally with two or more halogen atoms bridging the metal centers.…”

Section: Introductionmentioning

confidence: 99%

“…30 The electronic states of CaCl arise from Ca ϩ free ion states in the field of the Cl Ϫ ligand. The lowest lying transitions of the atomic ion Ca ϩ are (3d 3 Ϫ1 , is predominantly 4p in character rather than 3d, but it contains mixtures of other Ca ϩ orbitals as well. Ca 2 Cl 3 is the smallest neutral polyatomic alkaline-earth halide that can be modeled as an unpaired electron bound to a framework of closed shell ions, Ca ϩ2 and Cl Ϫ .…”

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

Electronic spectroscopy of the alkaline-earth halide cluster Ca2Cl3

Lobo

Deev

Wong

et al. 2001

A visible spectrum of the cluster Ca 2 Cl 3 was observed from 651 to 630 nm by 1ϩ1Ј resonant multiphoton ionization spectroscopy. Cl 3 . The spectra were composed of a strong origin band at 15 350.8 cm Ϫ1 and several very weak vibronic bands. All of the bands were sharp with partially resolved rotational band contours. Density functional calculations predicted three minimum energy isomers. The spectrum was assigned to the 2 B 2 ←X 2 A 1 transition of the lowest energy isomer, a planar C 2v structure having a ring of two Cl and two Ca atoms and a terminal Cl atom. The ring isomer of Ca 2 Cl 3 has the unpaired electron localized on one Ca 2ϩ ion to form a Ca ϩ chromophore. The two other predicted isomers, a D 3h trigonal bipyramid and a C 2v planar V-shaped structure, were not consistent with the observations.