H‐bond and electric field correlations for water in highly hydrated crystals

Abstract

We present periodic plane‐wave density functional theory (DFT) Perdew–Burke–Ernzerhof (PBE‐D2) calculations for four highly hydrated crystals, Na2CO3·10H2O, MgSO4·7H2O, MgSO4·11H2O, and Al(NO3)3·9H2O, containing 37 structurally unique water molecules and 74 unique hydrogen bonds. The calculated R(H···O) distances lie in the range 1.60–2.05 Å, the anharmonic OH frequencies in the range 2570–3425 cm−1, and the water dipole moments lie in the range 2.9–4.3 Debye, as calculated from the Wannier function centers and the nuclei. We present the following findings. (i) Our optimized intramolecular r(OH) distances are always larger than the gas‐phase value and thus more accurate than those derived from neutron diffraction experiments; (ii) The local in situ electric field over the molecule, calculated from the positions of the nuclei and the Wannier centers in the surrounding crystal, appears to be a good descriptor of the pertturbation from the water molecule's surroundings as the internal molecular properties (re, ν, μ) are found to correlate well with the crystal‐generated electric field; (iii) We have added DFT‐calculated data points to the well‐known experimental ‘OH frequency versus R(H···O)' correlation curve in a region where the experimental data points are scarce; (iv) For all 37 water molecules, the Wannier centers located in the lone‐pair region, and those located in the OH bonds, displace about equally much due to the polarizing environment. Finally, we propose that our resulting 'OH frequency versus Wannier‐type electric field' correlation curve may constitute a useful tool for predicting OH vibrational frequencies from snapshots from PBE‐D2‐based ab initio molecular dynamics simulations of water‐containing systems. © 2015 Wiley Periodicals, Inc.

Effects of H-bond asymmetry on the electronic properties of liquid water – An AIMD analysis

“…On average the water molecule is thus enhanced by a factor of more than 60% compared to the gas-phase value. This is a large increase, but much smaller than what has been shown to occur in simple ionic crystalline hydrates which can display Wannier-type water dipole moments well over 4 Debye [64][65].…”

Effect of aluminum vacancies on the H2O2 or H2O interaction with a gamma‐AlOOH surface. A solid‐state DFT study

“…The slab parameters are fixed, and structural relaxations are limited to the positional parameters of atoms. This is a typical approximation for the calculation of the molecular crystals and periodic systems with H‐bonds, since the change in the volume of a simulated cell appears to be insignificant after the full optimization of molecular crystals . BSSE‐corrected interaction energies between H 2 O/H 2 O 2 molecules and slabs were determined using the counterpoise method as implemented in the CRYSTAL09 suite.…”

Multi-Scale Modelling of Water and Hydroxide in Solids and Solutions

“…The reason behind these systematic experimental distance "errors" is known and was elaborated on in Ref. 6. The resulting 'r(OH) vs. R(O•••O)' correlation curve from the quantum-mechanical crystal calculations is shown in Figure 3c.…”

“…We have found that theoretical calculations for ionic hydrate crystals present a unique opportunity to gather novel information about the water molecule and its structure-property relations [6]. Ample high-quality structural data are available from diffraction experiments for a large number of crystalline hydrates where water coexists with metal ions, sulphates, nitrates, halides etc., and we, the modelers, can then focus on modelling the properties themselves.…”

“…In Figure 3b the results from the X-ray diffraction data-set have been removed, leaving only the three neutron diffraction studies. [6]. The figures display both the difference electron density (total electron density of the crystal minus the sum of the electron densities of the isolated building blocks) and the total dipole moment of the water molecules.…”