Quantum mechanical charge field molecular dynamics simulation of the TiO²⁺ ion in aqueous solution

Abstract

Structural and dynamical properties of the TiO(2+) ion in aqueous solution have been investigated by using the new ab initio quantum mechanical charge field (QMCF) molecular dynamics (MD) formalism, which does not require any other potential functions except those for solvent-solvent interactions. Both first and second hydration shell have been treated at Hartree-Fock (HF) quantum mechanical level. A Ti-O bond distance of 1.5 A was observed for the [Ti=O](2+) ion. The first hydration shell of the ion shows a varying coordination number ranging from 5 to 7, five being the dominant one and representing one axial and four equatorial water molecules directly coordinated to Ti, which are located at 2.3 A and 2.1 A, respectively. The flexibility in the coordination number reflects the fast exchange processes, which occur only at the oxo atom, where water ligands are weakly bound through hydrogen bonds. Considering the first shell hydration, the composition of the TiO(2+) hydrate can be characterized as [(H(2)O)(0.7)(H(2)O)(4) (eq)(H(2)O)(ax)](2+). The second shell consists in average of 12 water molecules located at a mean distance of 4.4 A. Several other structural parameters such as radial and angular distribution functions and coordination number distributions were analyzed to fully characterize the hydration structure of the TiO(2+) ion in aqueous solution. For the dynamics of the TiO(2+) ion, different sets of dynamical parameters such as Ti=O, Ti-O(eq), and Ti-O(ax) stretching frequencies and ligands' mean residence times were evaluated. During the simulation time of 15 ps, 3 water exchange processes in the first shell were observed at the oxo atom, corresponding to a mean residence time of 3.6 ps. The ligands' mean residence time for the second shell was determined as 3.5 ps.

The hydration properties of Gd(III) and Tb(III): An ab initio quantum mechanical molecular dynamics study

“…In this study the ab initio quantum mechanical charge-field molecular dynamics (QMCF-MD) approach [2,3] has been used as it had already yielded accurate insight into the hydration properties of a wide range of cations [4][5][6] and anions [7], as well as complexes [8][9][10]. In particular, a number of trivalent cations of the lanthanoide [11][12][13][14][15] and actinoide series [16] have already been successfully investigated, the results being in very good agreement with experimental data where available.…”

Structure and dynamics of phosphate ion in aqueous solution: An ab initio QMCF MD study

“…Ab initio quantum mechanical charge field (QMCF) molecular dynamics is a new simulation methodology for an accurate treatment of solvated compounds 7. This methodical framework is strongly related to the intensively used QM/MM scheme8, 9 and makes it possible to investigate structure and dynamics of composite ions in aqueous solution in a straigthforward way 2, 10. The simulation box is divided into three regions of different calculation level: the QM zones (core and layer) and the MM region.…”

Hydration of highly charged ions

“…Some of them immediately form oxonium ions ${\text{H}}_3{\text{O}}^{+}$ and are thus reduced to a lower charge state (vide infra), others are present as oxo-ions, e.g. ${\text{TiO}}_2^{+}$ [45]. There is experimental evidence, however, that zirconium, hafnium.…”