Application of the SCC-DFTB Method to Hydroxide Water Clusters and Aqueous Hydroxide Solutions

2013 ◽  
Vol 117 (17) ◽  
pp. 5165-5179 ◽  
Author(s):  
Tae Hoon Choi ◽  
Ruibin Liang ◽  
C. Mark Maupin ◽  
Gregory A. Voth
Keyword(s):  
Water Clusters ◽  
Hydroxide Water

Case Study of Autistic Subjects with Stable Water Clusters in Panama

2012 ◽  
Vol 3 (3-4) ◽  
pp. 267-280 ◽  
Author(s):  
Ricardo Velasquez ◽  
Holly Chu ◽  
Shui Yin Lo
Keyword(s):  
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.

Interaction of Gold Atom with Clusters of Water: Few Computational Mise-En-Scènes with Hydrogen Bonding Motif

2008 ◽  
Vol 73 (11) ◽  
pp. 1457-1474 ◽  
Author(s):  
Eugene S. Kryachko
Keyword(s):  
Hydrogen Bond ◽  
Hydrogen Bonding ◽  
Computational Model ◽  
Photoelectron Spectroscopy ◽  
Water Clusters ◽  
Gold Atom ◽  
Proton Acceptor ◽  
Anion Photoelectron Spectroscopy ◽  
Relationship Of ◽  
First Time

The present work outlines the fair relationship of the computational model with the experiments on anion photoelectron spectroscopy for the gold-water complexes [Au(H2O)1≤n≤2]- that is established between the auride anion Au- and water monomer and dimer thanks to the nonconventional hydrogen bond where Au- casts as the nonconventional proton acceptor. This work also extends the computational model to the larger complexes [Au(H2O)3≤n≤5]- where gold considerably thwarts the shape of water clusters and even particularly breaks their conventional hydrogen bonding patterns. The fascinating phenomenon of the lavish proton acceptor character of Au- to form at least six hydrogen bonds with molecules of water is computationally unveiled in the present work for the first time.

Important Roles of Water Clusters Confined in a Nanospace as Revealed by a Synchrotron X-ray Diffraction Study

Langmuir ◽  
2021 ◽  
Author(s):  
Tomohiko Okada ◽  
Kana Izumi ◽  
Shogo Kawaguchi ◽  
Chikako Moriyoshi ◽  
Takuya Fujimura ◽  
...  
Keyword(s):  
Diffraction Study ◽  
Water Clusters ◽  
X Ray Diffraction ◽  
X Ray

Simulation of UV Absorption Spectra and Relaxation Dynamics of Uracil and Uracil-Water Clusters

2020 ◽  
Author(s):  
Branislav Milovanović ◽  
Jurica Novak ◽  
Mihajlo Etinski ◽  
Wolfgang Domcke ◽  
Nadja Doslic
Keyword(s):  
Aqueous Solution ◽  
Gas Phase ◽  
Absorption Spectra ◽  
Absorption Spectroscopy ◽  
Water Clusters ◽  
Uv Absorption ◽  
Relaxation Dynamics ◽  
Nonradiative Relaxation ◽  
Uv Absorption Spectra ◽  
Uv Absorption Spectroscopy

Despite many studies, the mechanisms of nonradiative relaxation of uracil in the gas phase and in aqueous solution are still not fully resolved. Here we combine theoretical UV absorption spectroscopy...

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