The hydration of the uranyl dication: Incorporation of solvent effects in parallel density functional calculations with the program PARAGAUSS

Abstract

ABSTRACT:The parallel density functional program PARAGAUSS has been extended by a tool for computing solvent effects based on the conductor-like screening model (COSMO). The molecular cavity in the solvent is constructed as a set of overlapping spheres according to the GEPOL algorithm. The cavity tessellation scheme and the resulting set of point charges on the cavity surface comply with the point group symmetry of the solute. Symmetry is exploited to reduce the computational effort of the solvent model. To allow an automatic geometry optimization including solvent effects, care has been taken to avoid discontinuities due to the discretization (weights of tesserae, number of spheres created by GEPOL). In this context, an alternative definition for the grid points representing the tesserae is introduced. In addition to the COSMO model, short-range solvent effects are taken into account via a force field. We apply the solvent module to all-electron scalar-relativistic density functional calculations on uranyl, UO 2 2+ , and its aquo complexes in aqueous solution. Solvent effects on the geometry are very small. Based on the model [UO 2 (H 2 O) 5 ] 2+ , the solvation energy of uranyl is estimated to be about −400 kcal/mol, in agreement with the range of experimental data. The major part of the FUCHS, SHOR, AND RÖSCHsolvation energy, about −250 kcal/mol, is due to a donor-acceptor interaction associated with a coordination shell of five water ligands. One can interpret this large solvation energy also as a compounded effect of an effective reduction of the uranyl moiety plus a solvent polarization. The energetic effect of the structure relaxation in the solution is only about 8 kcal/mol.

Uranyl complexation by monodentate nitrogen donor ligands. A relativistic density functional study

“…Table IV collects the resulting charges of uranyl and its ligands H 2 O and L N . For solvated uranyl, the well known substantial donation of electron charge density, $0.24 e per aqua ligand, leads to a notable reduction of the charge of the uranyl moiety, from formal 2 e to 0.79 e [34,42,45,46]. Each ligand L N donates approximately the same amount of electron density, 0.25-0.26 e, to the uranyl moiety as an (average) aqua ligand of these complexes (Table IV).…”

“…For the largest component of the displacement gradients and the length of the update step, the convergence threshold was set to 10 À6 au for optimizations in the gas phase and to 10 À4 au for the solvent models. Long-range electrostatic solvation effects were modeled by the COSMO (conductor-like screening model) variant of the polarizable continuum model (PCM), as implemented in PARAGAUSS [34]. To achieve a sufficiently accurate representation of short-range solvation effects, also aqua ligands of the first solvation shell of uranyl were included in the quantum chemical model.…”

Uranyl Solvation by a Three-Dimensional Reference Interaction Site Model

“…[ , ] ( ) e e (5) where E[n e ,s] is the solute internal energy that depends on the solute's geometric degrees of freedom s and, in the case of a QM solute, also on the electronic density n e , but not on the solvent site distribution functions h. 55 The solvation energy of uranyl is estimated as , where E is the average configurational energy of a water molecule; its value is about −9.9 kcal/mol. 57,58 This result is to be compared to the solvation energy of −6.3 kcal/mol derived from the ratio of the equilibrium vapor/liquid concentrations.…”

Four-Component Relativistic Calculations in Solution with the Polarizable Continuum Model of Solvation: Theory, Implementation, and Application to the Group 16 Dihydrides H2X (X = O, S, Se, Te, Po)

“…Many applications in the calculation of structures and energetics of heavyelement containing species make use of effective core potentials (ECPs) in a DFT or wave function theory framework [25][26][27][28][29][30][31][32] . In other studies, the more refined Zeroth-Order Regular Approximation (ZORA) Hamiltonian 33 has been used, either in the scalar, spin-free form or in a 2-component framework, including spin-orbit effects [34][35][36][37][38][39] . The second-order DouglasKroll-Hess (DKH2) in spin-free form, has also been applied 40 In all aforementioned studies, bulk solvent effects, described by use of a continuum model such as COSMO, were found to be extremely important in order to achieve a qualitatively accurate description of the phenomena of interest.…”