Coupling a polarizable water model to the hydrated ion–water interaction potential: A test on the Cr3+ hydration

Abstract

A strategy to build interaction potentials for describing ionic hydration of highly charged monoatomic cations by computer simulations, including the polarizable character of the solvent, is proposed. The method is based on the hydrated ion concept that has been previously tested for the case of Cr 3ϩ aqueous solutions ͓J. Phys. Chem. 100, 11748 ͑1996͔͒. In the present work, the interaction potential of ͓Cr͑H 2 O 6 ͔͒ 3ϩ with water has been adapted to a water model that accounts for the polarizable character of the solvent by means of a mobile charge harmonic oscillator representation ͑MCHO model͒ ͓J. Chem. Phys. 93, 6448 ͑1990͔͒. Monte Carlo simulations of the Cr 3ϩ hexahydrate plus 512 water molecules have been performed to study the energetics and structure of the ionic solution. The results show a significant improvement in the estimate of the hydration enthalpy ͓⌬H hydr ͑Cr 3ϩ ͒ϭϪ1109.6Ϯ70 kcal/mol͔ that now matches the experimental value within the uncertainty of this magnitude. The use of the polarizable water model lowers by ϳ140 kcal/mol the statistical estimation of the ͓Cr͑H 2 O 6 ͔͒ 3ϩ hydration enthalpy compared to the nonpolarizable model. ͑Ϫ573 kcal/mol for the polarizable model vs Ϫ714 kcal/mol for the nonpolarizable one.͒ This improvement reflects a more accurate treatment of the many-body nonadditive effects.

Structure and dynamics of the Cr(III) ion in aqueous solution: Ab initio QM/MM molecular dynamics simulation

“…1,2 The octahedral structure of [Cr(H 2 O) 6 ] 3ϩ has been determined by several experimental techniques such as X-ray diffraction (XRD), [3][4][5] neutron diffraction (ND), 6,7 large-angle X-ray diffraction (LAXS), 8 and extended X-ray absorption fine structure (EXAFS) 9,10 methods. In theoretical investigations, Monte Carlo (MC) 11,12 and molecular dynamics (MD) [13][14][15] simulations based on numerous approaches of water-water interaction models and ion-water interaction potential construction have been performed to determine the structure of the second hydration shell of Cr(H 2 O) 6 3ϩ , keeping the Cr(III) ion's kinetically inert first hydration shell at a rigid geometry. By using variable high field 17 O NMR to observe fast ligand exchange processes between the second hydration shell and the bulk for the hydrated Cr(III) ion, the exchange rate k ex 298 of (7.8 Ϯ 0.2) ϫ 10 9 s Ϫ1 was obtained, corresponding to an average lifetime of 128 ps for water molecules in the second hydration shell.…”

QM/MM: what have we learned, where are we, and where do we go from here?

“…Schemes that relax this constraint can be called self-consistent embedding schemes (or polarized embedding schemes). However, self-consistency is difficult to achieve because it requires a polarizable MM force field [157][158][159][160][161][162][163][164][165][166][167][168][169], which has the flexibility to respond to perturbation by an external electric field. Such flexibility is not available in today's most popular MM force fields, although research to develop a polarizable force field has received much attention [164,166].…”

Ab-initio structure, energy and stable Cr isotopes equilibrium fractionation of some geochemically relevant H-O-Cr-Cl complexes

“…Investigating in detail the effect of the reaction field (2 nd and higher order shells) on a few representative Since the B3LYP/6-31G** IEFPCM and COSMO computations are plagued by convergence problems (not perceived at variational level but solely at the vibrational analysis), we attempted a simpler computational approach avoiding diffuse functions and performed an explicit solvation assuming the initial Cr[6-12] structure already investigated by Martinez et al (2000). The interaction energy between the Cr 3ϩ hexahydrate and its hydration shell, obtained from the Harthree-Fock energies of the interacting molecules: -electrostatic contributions).…”