scholarly journals First-Principles Study of AlPO4-H3, a Hydrated Aluminophosphate Zeotype Containing Two Different Types of Adsorbed Water Molecules

Molecules ◽  
2019 ◽  
Vol 24 (5) ◽  
pp. 922 ◽  
Author(s):  
Michael Fischer
Keyword(s):  
Density Functional ◽  
Computational Study ◽  
Pore Space ◽  
Experimental Studies ◽  
Adsorbed Water ◽  
Working Fluid ◽  
Water Molecules ◽  
Small Pore ◽  
Experimental Crystal ◽  
Heat Transformation

Porous aluminophosphate zeotypes (AlPOs) are promising materials for heat transformation applications using water as a working fluid. Two “types” of adsorbed water molecules can be distinguished in hydrated AlPOs: Water molecules adsorbed in the direct proximity of framework aluminium atoms form bonds to these Al atoms, with the coordination number of Al increasing from four to five or six. The remaining water molecules that are adsorbed in other parts of the accessible pore space are not strongly bonded to any framework atom, they interact with their environment exclusively through hydrogen bonds. The APC-type small-pore aluminophosphate AlPO4-H3 contains both types of H2O molecules. In the present work, this prototypical hydrated AlPO is studied using dispersion-corrected density functional theory (DFT) calculations. After validating the computations against experimental crystal structure and Raman spectroscopy data, three interrelated aspects are addressed: First, calculations for various partially hydrated models are used to establish that such partially hydrated phases are not thermodynamically stable, as the interaction with the adsorbed water molecules is distinctly weaker than in fully hydrated AlPO4-H3. Second, IR and Raman spectra are computed and compared to those of the dehydrated analogue AlPO4-C, leading to the identification of a few “fingerprint” modes that could be used as indicators for the presence of Al-coordinated water molecules. Finally, DFT-based molecular dynamics calculations are employed to study the dynamics of the adsorbed water molecules. All in all, this in-depth computational study of AlPO4-H3 contributes to the fundamental understanding of hydrated AlPOs, and should therefore provide valuable information for future computational and experimental studies of these systems.

First-Principles Study of AlPO4-H3, a Hydrated Aluminophosphate Zeotype Containing Two Different Types of Adsorbed Water Molecules

2019 ◽  
Author(s):  
Michael Fischer
Keyword(s):  
Density Functional ◽  
Computational Study ◽  
Pore Space ◽  
Experimental Studies ◽  
Adsorbed Water ◽  
Working Fluid ◽  
Water Molecules ◽  
Small Pore ◽  
Experimental Crystal ◽  
Heat Transformation

<div>Porous aluminophosphate zeotypes (AlPOs) are promising materials for heat transformation applications using water as a working fluid. Two "types" of adsorbed water molecules can be distinguished in hydrated AlPOs: Water molecules adsorbed in the direct proximity of framework aluminium atoms form bonds to these Al atoms, with the coordination number of Al increasing from four to five or six. The remaining water molecules that are adsorbed in other parts of the accessible pore space are not strongly bonded to any framework atom, they interact with their environment exclusively through hydrogen bonds. The APC-type small-pore aluminophosphate AlPO<sub>4</sub>-H3 contains both types of H<sub>2</sub>O molecules. In the present work, this prototypical hydrated AlPO is studied using dispersion-corrected density functional theory (DFT) calculations. After validating the computations against experimental crystal structure and Raman spectroscopy data, three interrelated aspects are addressed: First, calculations for various partially hydrated models are used to establish that such partially hydrated phases are not thermodynamically stable, as the interaction with the adsorbed water molecules is distinctly weaker than in fully hydrated AlPO<sub>4</sub>-H3. Second, IR and Raman spectra are computed and compared to those of the dehydrated analogue AlPO<sub>4</sub>-C, leading to the identification of a few "fingerprint" modes that could be used as indicators for the presence of Al-coordinated water molecules. Finally, DFT-based molecular dynamics calculations are employed to study the dynamics of the adsorbed water molecules. All in all, this in-depth computational study of AlPO<sub>4</sub>-H3 contributes to the fundamental understanding of hydrated AlPOs, and should therefore provide valuable information for future computational and experimental studies of these systems.</div>

First-Principles Study of AlPO4-H3, a Hydrated Aluminophosphate Zeotype Containing Two Different Types of Adsorbed Water Molecules

2019 ◽  
Author(s):  
Michael Fischer
Keyword(s):  
Density Functional ◽  
Computational Study ◽  
Pore Space ◽  
Experimental Studies ◽  
Adsorbed Water ◽  
Working Fluid ◽  
Water Molecules ◽  
Small Pore ◽  
Experimental Crystal ◽  
Heat Transformation

<div>Porous aluminophosphate zeotypes (AlPOs) are promising materials for heat transformation applications using water as a working fluid. Two "types" of adsorbed water molecules can be distinguished in hydrated AlPOs: Water molecules adsorbed in the direct proximity of framework aluminium atoms form bonds to these Al atoms, with the coordination number of Al increasing from four to five or six. The remaining water molecules that are adsorbed in other parts of the accessible pore space are not strongly bonded to any framework atom, they interact with their environment exclusively through hydrogen bonds. The APC-type small-pore aluminophosphate AlPO<sub>4</sub>-H3 contains both types of H<sub>2</sub>O molecules. In the present work, this prototypical hydrated AlPO is studied using dispersion-corrected density functional theory (DFT) calculations. After validating the computations against experimental crystal structure and Raman spectroscopy data, three interrelated aspects are addressed: First, calculations for various partially hydrated models are used to establish that such partially hydrated phases are not thermodynamically stable, as the interaction with the adsorbed water molecules is distinctly weaker than in fully hydrated AlPO<sub>4</sub>-H3. Second, IR and Raman spectra are computed and compared to those of the dehydrated analogue AlPO<sub>4</sub>-C, leading to the identification of a few "fingerprint" modes that could be used as indicators for the presence of Al-coordinated water molecules. Finally, DFT-based molecular dynamics calculations are employed to study the dynamics of the adsorbed water molecules. All in all, this in-depth computational study of AlPO<sub>4</sub>-H3 contributes to the fundamental understanding of hydrated AlPOs, and should therefore provide valuable information for future computational and experimental studies of these systems.</div>

First-Principles Study of AlPO4-H3, a Hydrated Aluminophosphate Zeotype Containing Two Different Types of Adsorbed Water Molecules

2019 ◽  
Author(s):  
Michael Fischer
Keyword(s):  
Crystal Structure ◽  
Density Functional ◽  
Computational Study ◽  
Pore Space ◽  
Experimental Studies ◽  
Adsorbed Water ◽  
Working Fluid ◽  
Water Molecules ◽  
Small Pore ◽  
Experimental Crystal

<div>Porous aluminophosphate zeotypes (AlPOs) are promising materials for heat transformation applications using water as a working fluid. Two "types" of adsorbed water molecules can be distinguished in hydrated AlPOs: Water molecules adsorbed in the direct proximity of framework aluminium atoms form bonds to these Al atoms, with the coordination number of Al increasing from four to five or six. The remaining water molecules that are adsorbed in other parts of the accessible pore space are not strongly bonded to any framework atom, they interact with their environment exclusively through hydrogen bonds. The APC-type AlPO<sub>4</sub>-H3, a small-pore aluminophosphate, contains both types of H<sub>2</sub>O molecules, and the locations of the water molecules in the crystal structure have been determined previously using single-crystal X-ray diffraction. In the present work, this prototypical hydrated AlPO is studied using dispersion-corrected density functional theory (DFT) calculations. After validating the computations against experimental crystal structure and Raman spectroscopy data, three interrelated aspects are addressed: First, calculations for various partially hydrated models are used to establish that such partially hydrated phases are not thermodynamically stable, as the interaction with the adsorbed water molecules is distinctly weaker than in fully hydrated AlPO<sub>4</sub>-H3. Second, IR and Raman spectra are computed and compared to those of the dehydrated analogue AlPO<sub>4</sub>-C, leading to the identification of a few "fingerprint" modes that could be used as indicators for the presence of Al-coordinated water molecules. Finally, DFT-based molecular dynamics calculations are employed to study the dynamics of the adsorbed water molecules. All in all, this in-depth computational study of AlPO<sub>4</sub>-H3 contributes to the fundamental understanding of hydrated AlPOs, and should therefore provide valuable information for future computational and experimental studies of these systems.</div>

scholarly journals Computational Study of some Double Headed Acyclo-C-Nucleosides

2015 ◽  
Vol 61 ◽  
pp. 1-11
Author(s):  
Sarah Amara ◽  
Noureddine Tchouar ◽  
Salah Belaidi
Keyword(s):  
Electronic Properties ◽  
Ground State ◽  
Density Functional ◽  
Computational Study ◽  
Experimental Studies ◽  
Functional Theory ◽  
Hartree Fock ◽  
Structural And Electronic Properties ◽  
Semi Empirical

In the present paper we have a focus in a study of theoretical characterization of three double headed acyclo-C-nucleosides, which are a recent target of experimental studies. The structural and electronic properties of double headed acyclo-C-nucleosides, 1,4-bis (3-mercapto-1H-1,2,4-triazol-5-yl) butane-1,2,3,4-tetrol, 1,4-bis (4-amino-5-mercapto-4H-1,2,4-triazol-3-yl) butane-1,2,3,4-tetrol and 5,5'-(1,2,3,4-tetrahydroxybutane-1,4-diyl) bis (1,3,4-oxadiazole-2(3H)-thione), have been investigated theoretically by performing semi-empirical molecular orbital, ab initio Hartree-Fock (HF) and Density Functional Theory (DFT) calculations. Geometries of the three molecules are optimized at the level of Austin Model 1 (AM1). The electronic properties and relative energies of the molecules have been calculated by HF and DFT in the ground state.

Insights into the Adsorption of Water and Oxygen on the Cubic CsPbBr3 Surfaces: A First-Principle Study

2021 ◽  
Author(s):  
Xin Zhang ◽  
Ruge Quhe ◽  
Ming Lei
Keyword(s):  
Adsorption Energy ◽  
Density Functional ◽  
Degradation Mechanism ◽  
Perovskite Solar Cells ◽  
Density Functional Theory Calculations ◽  
Adsorbed Water ◽  
Energy Difference ◽  
Device Fabrication ◽  
Water Molecules ◽  
Inorganic Perovskite

Abstract The degradation mechanism of the all-inorganic perovskite solar cells in the ambient environment remains unclear. In this paper, water and oxygen molecule adsorptions on the all-inorganic perovskite (CsPbBr3) surface are studied by density-functional theory calculations. In terms of the adsorption energy, the water molecules are more susceptible than the oxygen molecules to be adsorbed on the CsPbBr3 surface. The water molecules can be adsorbed on both the CsBr- and PbBr-terminated surfaces, but the oxygen molecules tend to be selectively adsorbed on the CsBr-terminated surface instead of the PbBr-terminated one due to the significant adsorption energy difference. While the adsorbed water molecules only contribute deep states, the oxygen molecules introduce interfacial states inside the bandgap of the perovskite, which would significantly impact the chemical and transport properties of the perovskite. Therefore, special attention should be paid to reduce the oxygen concentration in the environment during the device fabrication process so as to improve the stability and performance of the CsPbBr3 based devices.

scholarly journals Density Functional Theory Study of Bone Tissues: the Role of Water in Conferring Bone Strength

2020 ◽  
Vol 2 (2) ◽  
pp. 25
Keyword(s):  
Bone Strength ◽  
Density Functional ◽  
Water Adsorption ◽  
Experimental Studies ◽  
Bound Water ◽  
Adsorbed Water ◽  
Functional Theory ◽  
Explicit Solvent ◽  
Human Collagen

The unsurpassed mechanical properties of biomaterials stem from the intricate organization of inorganic and organic matter across length scales. In bone, water facilitates this organization, thereby playing an important structural role in addition to being a nutrient and waste transport medium. Water makes 10% of mammalian bone tissues and can be found in one of two states: bound (to the mineral phase) or mobile. While experimental studies were able to directly link the amount of bound water to bone strength, a molecular understanding of the interactions between the mineral (hydroxyapatite), organic (collagen) phase, and water is missing. In this talk, I will provide new insights into the water adsorption properties of bone tissues. I will present DFT calculations of water adsorption energy as a function of the environment, which includes an explicit solvent and human collagen fragments. I will show that the environment - rather than the mineral surface itself-governs the adsorption strength and mode. In particular, I will show that conditions consistent with aging tissues are associated with a lower density of adsorbed water molecules, which is a sign of weaker bones.

scholarly journals Computational Study of the Structure of a Sepiolite/Thioindigo Mayan Pigment

2012 ◽  
Vol 2012 ◽  
pp. 1-6 ◽  
Author(s):  
Manuel Alvarado ◽  
Russell C. Chianelli ◽  
Roy M. Arrowood
Keyword(s):  
Density Functional Theory ◽  
Density Functional ◽  
Color Change ◽  
Computational Study ◽  
Experimental Studies ◽  
Computational Studies ◽  
Molecular Orbital Theory ◽  
Orbital Theory ◽  
Functional Theory ◽  
Best Fit

The interaction of thioindigo and the phyllosilicate clay sepiolite is investigated using density functional theory (DFT) and molecular orbital theory (MO). The best fit to experimental UV/Vis spectra occurs when a single thioindigo molecule attaches via Van der Waals forces to a tetrahedrally coordinated cation with an additional nearby tetrahedrally coordinated also present. The thioindigo molecule distorts from its planar structure, a behavior consistent with a color change. Due to the weak interaction between thioindigo and sepiolite we conclude that the thioindigo molecule must be trapped in a channel, an observation consistent with previous experimental studies. Future computational studies will look at the interaction of indigo with sepiolite.

scholarly journals Computational and Experimental Studies of Biolubricant Stability Derived from Oleic Acid

2020 ◽  
Vol 3 (3) ◽  
pp. 139
Author(s):  
Yehezkiel Steven Kurniawan ◽  
Hendra ◽  
Tutik Dwi Wahyuningsih
Keyword(s):  
Oleic Acid ◽  
Internal Energy ◽  
Density Functional ◽  
Computational Study ◽  
Experimental Studies ◽  
The Other ◽  
Basis Set ◽  
Dihydroxystearic Acid ◽  
Base Number ◽  
Energy Value

In the present work, the stability of six biolubricant compounds, i.e. Acetal, Ketal, D[4.4], D[4.5], Cyclic-6, and Cyclic-7, was evaluated both theoretically and experimentally. These compounds were prepared from oleic acid through hydroxylation and esterification reactions. The computational study of the compounds was conducted by using the Density Functional Theory (DFT) method at B3LYP level of theory and 6-31 G (d,p) basis set. The theoretical stability was reflected from the internal energy value of the hydrolysis reaction of the biolubricant compounds to form the 9,10-dihydroxystearic acid. The order of stability is given as follows: Cyclic-6 (-3.458 kJ/mol) > Acetal (-3.446  kJ/mol) > Cyclic-7 (-3.364  kJ/mol) > D[4.5] (-3.343  kJ/mol) > D[4.4] (-3.261 kJ/mol) > Ketal (-3.058 kJ/mol). On the other hand, the experimental stability of the biolubricant compounds was measured using the American Society for Testing and Material (ASTM) standard method for total acid number (TAN) and total base number (TBN). It was found that the Cyclic-6 derivative yielded the lowest TAN (1.37 mg KOH/g) and TBN (3.53 mg KOH/g) values compared to the other biolubricant compounds. Meanwhile, the Cyclic-6 also showed the lowest internal energy value (-3.458 kJ/mol) from the computational study due to the high stability of six-membered ring. These results reveal that the experimental TAN and TBN values could be predicted from the theoretical internal energy value, i.e. TAN (mg KOH/g) = 35.183 (DE) – 123.02 (R2 = 0.9226) and TBN (mg KOH/g) = 105.71 (DE) – 369.72 (R2 = 0.8946), which is remarkable.

Structure and bonding of water molecules in zeolite hosts: Benchmarking plane-wave DFT against crystal structure data

2015 ◽  
Vol 230 (5) ◽  
Author(s):  
Michael Fischer
Keyword(s):  
Plane Wave ◽  
Structure Data ◽  
Density Functional ◽  
Detailed Comparison ◽  
Water Molecules ◽  
Functional Theory ◽  
Interatomic Distances ◽  
Cell Parameters ◽  
Structure Determinations ◽  
Experimental Crystal

AbstractDensity-functional theory (DFT) calculations are widely employed to study the interaction of water molecules with zeolite frameworks. However, there have been only few attempts to assess whether these computations reproduce experimental structure data sufficiently well, especially with regard to the hydrogen positions of the water molecules. In this work, a detailed comparison between experimental crystal structures and DFT-optimised structures is made for six water-loaded natural zeolites. For each system, high-quality structure determinations from neutron diffraction data have been reported (bikitaite/Li–BIK, edingtonite/Ba–EDI, gismondine/Ca–GIS, scolecite/Ca–NAT, natrolite/Na–NAT, yugawaralite/Ca–YUG). Using a plane-wave DFT approach, the performance of six pure and three dispersion-corrected exchange-correlation functionals is compared, focusing on an optimisation of the atomic coordinates in a fixed unit cell (with cell parameters taken from experiment). It is found that the PBE and the PW91 functional give the smallest overall deviation between experiment and computation. Of the dispersion-corrected approaches, the PBE–TS functional exhibits the best performance. For the PBE and PBE–TS functionals, the agreement between experiment and DFT is analysed in more detail for different groups of interatomic distances. Regarding the OW–H distances in the water molecules, the DFT optimisations lead to physically realistic bond lengths. On the other hand, DFT has a systematic tendency to underestimate the length of hydrogen bonds. The cation-oxygen distances are mostly in very good agreement with experiment, although some exceptions indicate the necessity of further studies.

scholarly journals The Polymorphs of ROY: A Computational Study of Lattice Energies and Conformational Energy Differences

2018 ◽  
Vol 71 (4) ◽  
pp. 279 ◽  
Author(s):  
Sajesh P. Thomas ◽  
Mark A. Spackman
Keyword(s):  
Density Functional Theory ◽  
Density Functional ◽  
Systematic Approach ◽  
Computational Study ◽  
Structural Diversity ◽  
Conformational Energy ◽  
Energy Calculation ◽  
Functional Theory ◽  
Lattice Energies ◽  
Experimental Crystal

The remarkable structural diversity observed in polymorphs of 5-methyl-2-[(2-nitrophenyl)amino]-3-thiophenecarbonitrile (commonly known as ROY) challenges computational attempts to predict or rationalize their relative stability. This modest study explores the applicability of CE-B3LYP model energy calculation of lattice energies (using experimental crystal structures), supplemented by a systematic approach to account for conformational energy differences. The CE-B3LYP model provides sensible estimates of absolute and relative lattice energies for the polymorphs, provided care is taken to achieve convergence in the summation of pairwise terms. Conformational energy differences based on density functional theory (DFT) energies are shown to be unreliable, but MP2 energies based on DFT-optimized structures show considerable promise.

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