Beryllium(II): The Strongest Structure-Forming Ion in Water? A QMCF MD Simulation Study

Abstract

A quantum mechanical charge field (QMCF) molecular dynamics (MD) simulation including the first and second hydration shells in the QM region has been carried out to describe the structural and dynamical properties of Be(2+) in aqueous solution. In this methodology, the full first and second hydration shells are treated by ab initio quantum mechanics supplemented by a fluctuating electrostatic embedding technique. From the simulation, structural properties were extracted and were found to be in good agreement with previously published experimental and theoretical results. The radial distribution function (RDF) showed the maximum probability of the Be-O bond length at 1.62 A. The first tetrahedrally arranged hydration shell is highly inert with respect to ligand-exchange processes. Application of local-density-corrected three-body correlation analysis showed minor structural influence of the ion beyond the second hydration layer, contrary to the findings of a previous QM/MM MD simulation. The dynamics of the hydrate were studied in terms of ligand mean residence times (MRTs) and the power spectrum of the Be(2+)-O stretching frequency. A comparison of the "classical" QM/MM framework with the QMCF method clearly demonstrated the advantages of the latter, as ambiguities arising from the coupling of the subregions occurring in QM/MM MD simulations did not appear when the QMCF ansatz was applied.

An ab initio study of beryllium(II) hydration

“…Most of the various molecular dynamics simulations that correctly reproduce the tetrahydrate, give the most probable and/or mean Be-O distance of between 1.61-1.66 Å, with standard deviations of around 0.04-0.06 Å (Table 1). However, the vibrational spectrum as predicted by MD [28] is inadequate in our opinion for two reasons. First, the authors use a scaling factor of 0.89, which is normally meant to correct for the anharmonicity of the vibration and the deficiencies of the model.…”

“…Surprisingly, a classical MD simulation using Lennard-Jones and Coluombic potential two-body terms only was able to reproduce reasonably the hydration number and Be-O distance [27]. The QMCF method of Rode also gave a short Be-O distance [28]. To summarize, it appears that the sp-part of the basis set and the influence of the environment appear to be more important than correlation or polarization functions in predicting the Be-O distance in solution.…”

Perspectives for hybrid ab initio/molecular mechanical simulations of solutions: from complex chemistry to proton-transfer reactions and interfaces

“…The usefulness of a QM description becomes evident when treating systems exhibiting an anisotropic potential such as the transition-metal ions copper(II) [61], palladium(II) [62], and platinum(II) [63] and systems carrying lone-electron pairs, e.g., germanium(II) [64], tin(II) [65], and lead(II) [66] (see Fig. 2a and b).…”

A brighter beryllium

“…Research carried out 2 on tetracoordinated complexes, for example, has provided further knowledge of the structural diversity of beryllium complexes. The possible coordination numbers of beryllium have also recently been clarified 3,4 and mechanistic studies are underway to elucidate solvent-exchange processes 5,6 .…”