Which Density Functional Should Be Used to Describe Protonated Water Clusters?

2017 ◽  
Vol 121 (16) ◽  
pp. 3117-3127 ◽  
Author(s):  
Ruili Shi ◽  
Xiaoming Huang ◽  
Yan Su ◽  
Hai-Gang Lu ◽  
Si-Dian Li ◽  
...  
Keyword(s):  
Density Functional ◽  
Water Clusters

Proton Acidity and Proton Mobility in ECR-40, a Silicoaluminophosphate That Violates Löwenstein’s Rule

2019 ◽  
Author(s):  
Michael Fischer
Keyword(s):  
Density Functional ◽  
Water Clusters ◽  
Computational Study ◽  
Acid Catalyst ◽  
Ab Initio Molecular Dynamics ◽  
Brønsted Acidity ◽  
Hydrothermal Route ◽  
Proton Mobility ◽  
Brönsted Acidity ◽  
A Minor

<p>The silicoaluminophosphate zeotype ECR-40, which has the MEI topology, contains linkages of AlO<sub>4</sub> tetrahedra via a common oxygen atom, thereby violating the famous “Löwenstein’s rule”. Due to the proven existence of Al-O-Al linkages in this material, it constitutes an ideal model system to study the acidity and mobility of protons associated with such unusual linkages. In addition, their properties can be directly compared to those of protons associated with more common Si-O-Al linkages, which are also present in ECR-40. In this work, static density functional theory (DFT) calculations including a dispersion correction were employed to study the preferred proton sites as well as the Brønsted acidity of the framework protons, followed by DFT-based ab-initio molecular dynamics (AIMD) to investigate the proton mobility in guest-free and hydrated ECR-40. Initially, two different proton arrangements were compared, one containing both H[O6] protons associated with Al-O-Al linkages and H[O10] protons at Si-O-Al linkages, the other one containing only H[O10] protons. The former model was found to be thermodynamically favoured, as a removal of protons from the Al-O-Al linkages causes a local accumulation of negative charge. Calculations of the deprotonation energy showed a moderately higher Brønsted acidity of the H[O10] protons, at variance with previous empirical explanations, which attributed the exceptional performance of ECR-40 as acid catalyst to the presence of Al‑O‑Al linkages. The AIMD simulations (<i>T</i> = 298 K) delivered no appreciable proton mobility for guest-free ECR-40 and for low levels of hydration (one H<sub>2</sub>O per framework proton). Under saturation conditions, framework deprotonation occurred, leading to the formation of protonated water clusters in the pores. Pronounced differences between the two types of framework protons were observed: While the H[O10] protons were always removed from the Si-O-Al linkages, the Al-O-Al linkages remained mostly protonated, but deprotonation did occur to a minor extent. The observation of a degree of framework deprotonation of Al-O-Al linkages differs from the findings reported in a recent computational study of hydrated aluminosilicate zeolites with such linkages (Heard et al., <i>Chem. Sci.</i> <b>2019</b>, <i>10</i>, 5705), pointing to an influence of the overall framework composition. Further inspection of the AIMD results showed that a coordination of water molecules to framework Al atoms occurred in many cases, especially in the vicinity of the Al-O-Al linkages, sometimes resulting in a pronounced modification of the linkages through additional bridging oxygen atoms. Given the changes in the local structure, it can be expected that such modified linkages are especially prone to break upon dehydration. Thus, in addition to elucidating the deprotonation behaviour of protons associated with different types of linkages, the calculations also provide insights into possible reasons for the instability of Al-O-Al linkages, clarifying why Löwenstein’s rule is mostly obeyed in materials that are formed via a hydrothermal route.</p>

Reciprocal Polarizable Embedding with a Transferable H2O Potential Function II: Application to (H2O)n Clusters & Liquid Water

2019 ◽  
Author(s):  
Asmus Ougaard Dohn ◽  
Elvar Jónsson ◽  
Hannes Jonsson
Keyword(s):  
Density Functional Theory ◽  
Liquid Water ◽  
Density Functional ◽  
Water Clusters ◽  
Theory Model ◽  
Coupling Scheme ◽  
Functional Theory ◽  
Total Polarization ◽  
Electrostatic Embedding ◽  
Polarizable Embedding

The manuscript analyzes the accuracy of our recently developed reciprocal polarizable embedding scheme, where a density functional theory model of the QM region is coupled to a dipole- and quadrupole polarizable water potential of the MM region. We present calculations of water clusters and liquid water where we analyze the energy, atomic forces and total polarization to demonstrate that artifacts in energy and polarization introduced by the QM/MM coupling are small and well-behaved. Furthermore, our methodology improves the consistency of the structure of optimized water hexamer geometries when compared to results obtained with models that neglect polarization. Additionally, the manuscript provides evidence that our coupling scheme eliminates artifacts in the structure of liquid water obtained with simpler electrostatic embedding models.

What is the best density functional to describe water clusters: evaluation of widely used density functionals with various basis sets for (H2O) n (n = 1–10)

2011 ◽  
Vol 130 (2-3) ◽  
pp. 341-352 ◽  
Author(s):  
Fengyu Li ◽  
Lu Wang ◽  
Jijun Zhao ◽  
John Rui-Hua Xie ◽  
Kevin E. Riley ◽  
...  
Keyword(s):  
Density Functional ◽  
Water Clusters ◽  
Basis Sets ◽  
Density Functionals

HYDRATION AND DISSOCIATION OF CALCIUM HYDROXIDE IN WATER CLUSTERS: A QUANTUM CHEMICAL STUDY

2007 ◽  
Vol 06 (03) ◽  
pp. 595-609 ◽  
Author(s):  
CLARA JIAYUN MEN ◽  
FU-MING TAO
Keyword(s):  
Calcium Hydroxide ◽  
Quantum Chemical ◽  
Density Functional ◽  
Water Clusters ◽  
Quantum Chemical Study ◽  
Chemical Study ◽  
Structure Stability ◽  
Water Molecules ◽  
Aerosol Formation ◽  
Hydrated Clusters

The structure, stability, and properties of the hydrated clusters of calcium hydroxide, Ca ( OH )2( H 2 O )n, n = 1–6, were investigated using density functional and ab initio quantum chemical methods. The results show that six water molecules are needed to result in the complete dissociation of Ca ( OH )2. The stable and ionic conformer of Ca ( OH )2( H 2 O )6 has C 3 symmetry. Its surprising stability and high IR activity render hydrated clusters of Ca ( OH )2 potentially significant in the nucleation of noctilucent clouds in the mesosphere. Trends in the interaction energies (ΔEe) of the complexes show that water molecules in the first shell of Ca 2+ are highly stable, further alluding to the role of hydrated Ca ( OH )2 in aerosol formation.

Density-functional study of hydration of ammonium in water clusters

1999 ◽  
Vol 110 (10) ◽  
pp. 4734-4736 ◽  
Author(s):  
Filippo Brugé ◽  
Marco Bernasconi ◽  
Michele Parrinello
Keyword(s):  
Density Functional ◽  
Water Clusters ◽  
Functional Study ◽  
Density Functional Study
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