Building a polarizable pair interaction potential for lanthanoids(III) in liquid water: A molecular dynamics study of structure and dynamics of the whole series

Abstract

In this work we have extended our previously presented polarizable pair interaction potential for La(3+)-water [Duvail et al., J. Chem. Phys. 127, 034503 (2007)] to the whole lanthanoid(III) series (Ln(3+)) interacting with water. This was performed taking into account known modification of ionic radius and atomic polarizability across the series and thus changing potential parameters according to that. Our procedure avoids the hard task of doing expensive high level ab initio calculations for all the atoms in the series and provides results in good agreement with experimental data and with ab initio calculations performed on the last atom in the series (Lu(3+), the atom for which the extrapolation should be in principle much crude). Thus we have studied the hydration properties of the whole Ln(3+) series by performing classical molecular dynamics in liquid phase. This systematic study allows us to rationalize from a microscopic point of view the different experimental results on Ln(3+)-water distances, first shell coordination numbers and first shell water self-exchange reactivity. In particular, we found that across the series the coordination number decreases from 9 for light lanthanoids to 8 for heavy lanthanoids in a continuous shape. This is due to the continuous changing in relative stability of the two forms that can be both populated at finite temperature with different probabilities as a function of the Ln(3+) atomic number. The changeover of the Ln(3+) ionic radius across the series resulted to be the main driving physical properties governing not always the Ln(3+)-water distance changing across the series but also the observed coordination number and consequently ligand dynamics.

Fragment Molecular Orbital-Based Molecular Dynamics Study on Hydrated Ln(III) Ions

“…2). Duvail et al reported the ADF peak values of 70 degree and 137 degree for La(III) [22] and 74 degree and 143 degree for Lu(III) [27], and these values compare well with ours in Fig. 5.…”

“…These observations are in line with the RDF results (Fig. 4), again indicating that the gadolinium break [8][9][10][11][12] is not a sudden but smooth change in the hydrations of intermediate Ln(III) [24,27]. …”

“…5 plots the ADFs of La(III) and Lu(III). The first peak positions are in accord with the characteristic TTP and SAP structures [12,22,24,27], as expected. The shape of the first peak of Lu(III) is sharper than that of La(III), suggesting the tighter frame of the former.…”

“…The gadolinium break [8][9][10][11][12] was assessed with Eu(III), Gd(III) and Tb(III), and then no sudden change was found in both RDF and ADF results as reported in Ref. [24,27]. As a future project, the correlated (thus more costly) FMO-MD method [58] will be applied to the hydrated Ln(III) systems, possibly in the periodic boundary condition [59].…”

“…So far, an amount of simulations covering classical molecular mechanical (MM) MD, quantum mechanical (QM) and plane-wave type Car-Parrinello MD (CPMD) [16] and hybrid QM/MM MD have been reported on the hydrated Ln(III) ions [17][18][19][20][21][22][23][24][25][26][27][28][29][30][31][32][33][34]. A notable merit of CPMD is that it can directly handle electronic properties [17,18,23,29] at sizable computational costs.…”