scholarly journals Combined Molecular Dynamics and DFT Simulation Study of the Molecular and Polymer Properties of a Catechol-Based Cyclic Oligomer of Polyether Ether Ketone

Polymers ◽  
2020 ◽  
Vol 12 (5) ◽  
pp. 1054
Author(s):  
Pradeep R. Varadwaj
Keyword(s):  
Molecular Dynamics ◽  
Density Functional ◽  
Noncovalent Interactions ◽  
Supramolecular Assembly ◽  
Binary Complex ◽  
Cyclic Oligomer ◽  
Polyether Ether Ketone ◽  
Wide Range ◽  
Ether Ketone ◽  
The Individual

The geometrical, energetic, noncovalent, and material properties of a catechol-based cyclic oligomer of Polyether Ether Ketone (PEEK) called o-PEEK were investigated using Molecular Dynamics (MD) and Density Functional Theory (DFT) simulations. The DFT (and MD) calculation performed with the PBEsol functional (and COMPASS II force field) gave a density of 1.39 (and 1.36) gcm−3 and a volume of 2744.5 (and 2808.5) cm3 for o-PEEK and are comparable with the corresponding experimental values of 1.328 gcm−3 and 2884.6 cm3, respectively. The absolute values of the glass transition temperature (Tg) MD simulated using the unit-cell and 2 × 2 × 2 supercell geometries of the o-PEEK system were 424.4 and 428.6 K, respectively. Although these values slightly differ from each other, both are close to the experiment (Tg = 418.2 K). The results of the (charge) density gradient analysis suggest that the supramolecular assembly between the o-PEEK oligomers in the experimentally observed infinite semi-crystal is driven by a wide range of noncovalent interactions. While the individual local interactions between the oligomers were recognized to be weak-to-medium in strength and are theoretically difficult to quantify, the B97-D3/cc-pVTZ level stabilization energy responsible for the formation of each of the five binary complex configurations extracted from the PBEsol relaxed 2 × 2 × 2 supercell geometry of the o-PEEK system was calculated to vary between –3.5 and –33.0 kcal mol−1.

scholarly journals Calculation of the Detonation State of HN3 with Quantum Accuracy

2020 ◽  
Author(s):  
Cong Huy Pham ◽  
Rebecca Lindsey ◽  
Laurence E. Fried ◽  
Nir Goldman
Keyword(s):  
Molecular Dynamics ◽  
Density Functional Theory ◽  
Potential Energy ◽  
Force Field ◽  
Density Functional ◽  
Energy Surface ◽  
Detonation Properties ◽  
Training Set ◽  
Functional Theory ◽  
Wide Range

<div>HN<sub>3</sub> is a unique liquid energetic material that exhibits ultrafast detonation chemistry and a transition to metallic states during detonation. We combine the ChIMES many-body reactive force field and the extended-Lagrangian multiscale shock technique (MSST) molecular dynamics method to calculate the detonation properties of HN<sub>3</sub> with the accuracy of Kohn-Sham density-functional theory. ChIMES is based on a Chebyshev polynomial expansion and can accurately reproduce density-functional theory molecular dynamics (DFT-MD) simulations for a wide range of unreactive and decomposition conditions of liquid HN<sub>3</sub>. We show that addition of random displacement configurations and the energies of gas-phase equilibrium products in the training set allows ChIMES to efficiently explore the complex potential energy surface. Schemes for selecting force field parameters and the inclusion of stress tensor and energy data in the training set are examined. Structural and dynamical properties, as well as chemistry predictions for the resulting models are benchmarked against DFT-MD. We demonstrate that the inclusion of explicit four-body energy terms is necessary to capture the potential energy surface across a wide range of conditions. The present force field, which was fit to a balance of forces, energies, and stress tensors yields excellent agreement with DFT, while exhibiting an orders-of-magnitude increase in computational efficiency over DFT-MD. Our results generally retain the accuracy of DFT-MD while yielding a high degree of computational efficiency, allowing simulations to approach orders of magnitude larger time and spatial scales. The techniques and recipes for MD model creation we present allow for direct simulation of nanosecond shock compression experiments and calculation of the detonation properties of materials with the accuracy of Kohn-Sham density-functional theory.</div>

scholarly journals Modelling IR Spectra of Sulfonated Polyether Ether Ketone (SPEEK) Membranes for Fuel Cells

2020 ◽  
Vol 850 ◽  
pp. 138-143
Author(s):  
Guntars Vaivars ◽  
Kristīne Krūkle-Bērziņa ◽  
Madara Markus
Keyword(s):  
Ir Spectra ◽  
Density Functional ◽  
Cross Linking ◽  
Experimental Ir ◽  
Functional Theory ◽  
Polyether Ether Ketone ◽  
Sulfonated Polyether Ether Ketone ◽  
Membrane Geometry ◽  
Ether Ketone ◽  
Speek Membrane

SPEEK (sulfonated polyether ether ketone) membranes have been prepared and characterized. The SPEEK membrane geometry and theoretical vibration spectra calculated using density functional theory (DFT) as depending from membrane chain length and polymer cross-linking. Analyzed the limitations of the method by comparing theoretical and experimental IR spectra.

Ab Initio Molecular Dynamics Reveals New Active Sites in Atomically Dispersed Pt1/TiO2 Catalysts

2020 ◽  
Author(s):  
Nicholas Humphrey ◽  
Selin Bac ◽  
Shaama Mallikarjun Sharada
Keyword(s):  
Molecular Dynamics ◽  
Ab Initio ◽  
Active Sites ◽  
Density Functional ◽  
Elevated Temperatures ◽  
Water Gas Shift ◽  
Ab Initio Molecular Dynamics ◽  
Catalytic Surface ◽  
Wide Range ◽  
Water Gas

<div> <div> <div> <p>We present a multi-scale modeling study of atomically dispersed Pt on the (110) surface of rutile TiO2. Using density functional theory (DFT) and ab initio molecular dynamics (AIMD), we probe the dynamic evolution of the catalytic surface at elevated temperatures. We identify metal atom diffusion as well as support atom mobility as important dynamical phenomena that enable the formation of new active sites. Among the eight new dynamically formed sites that are distinct from prior experimental and DFT reports, two sites exhibit anionic, near-linear O−Pt−O configurations. Such configurations are neither intuitive nor easily located using static methods such as DFT. Therefore, DFT alone is not sufficient to obtain a complete, dynamic description of the catalytic surface. Furthermore, the near-linear O−Pt−O sites exhibit CO binding characteristics that are markedly distinct from their parent sites, with possibly higher activity towards CO oxidation and water-gas shift reactions. Based on the wide range of adsorbate affinities exhibited by the DFT and AIMD-generated sites in this study, our aim going forward is to probe site-sensitivity of water-gas shift kinetics with these catalysts. </p> </div> </div> </div>

scholarly journals Dielectric spectroscopy and thermally stimulated discharge current in PEEK film

2003 ◽  
Vol 28 (2) ◽  
pp. 49-53 ◽  
Author(s):  
W. K. Sakamoto
Keyword(s):  
Activation Energy ◽  
Discharge Current ◽  
Conduction Mechanism ◽  
Low Frequency ◽  
Synthetic Polymers ◽  
Polyether Ether Ketone ◽  
Space Charges ◽  
Wide Range ◽  
Thermally Stimulated Discharge Current ◽  
Ether Ketone

The complex permittivity of films of polyether ether ketone (PEEK) has been investigated over a wide range of frequency. There is no relaxation peak in the range of 1Hz to 10(5) Hz but in the low-frequency side (10-4 Hz) there is an evidence of a peak that also can be observed by thermally stimulated discharge current measurements. That peak is related with the glass transition temperature (Tg) of the polymer. The activation energy of the relaxation was found to be 0.44 eV, similar to that of several synthetic polymers. Space charges are important in the conduction mechanism as shown by discharging transient.

scholarly journals Noncovalent Interactions of 1,4-Dithiafulvene and Nitroaromatics: A Combined DFT and Ab Initio Molecular Dynamics (AIMD) Study

2021 ◽  
Author(s):  
Yuming Zhao ◽  
Cody Marcus King-Poole
Keyword(s):  
Molecular Dynamics ◽  
Ab Initio ◽  
Density Functional ◽  
Rational Design ◽  
Environmental Control ◽  
Noncovalent Interactions ◽  
Picric Acid ◽  
Decomposition Analysis ◽  
Ab Initio Molecular Dynamics ◽  
Energy Decomposition Analysis

The noncovalent interactions between a redox-active molecule, phenyl-substituted dithiafulvene (Ph-DTF), and ten commonly encountered nitroaromatic compounds (NACs) were systematically investigated by means of density functional theory (DFT) calculations and ab initio molecular dynamics (AIMD) simulations. Our modeling studies examined their 1:1 complexes in terms of equilibrium geometries, frontier molecular orbitals (FMOs), nature of noncovalent forces, intermolecular charge transfer (ICT), interaction energies and related energy decomposition analysis. The computational results indicate that Ph-DTF can form thermodynamically stable supramolecular complexes with trinitro-substituted benzenes (e.g., 2,4,6-trinisuchtrotoluene and picric acid), but its interactions with mono- and dinitrobenzenes do not exhibit such stability. The selective binding properties are further corroborated by AIMD simulations. Overall, this computational work establishes a comprehensive understanding of the nature of noncovalent interactions of Ph-DTF with various NACs, and the results can be used as theoretical guidance for the rational design of selective receptors and/or chemosensors for certain NACs that are of great concern in current industrial applications and environmental control.

scholarly journals Calculation of the Detonation State of HN3 with Quantum Accuracy

2020 ◽  
Author(s):  
Cong Huy Pham ◽  
Rebecca Lindsey ◽  
Laurence E. Fried ◽  
Nir Goldman
Keyword(s):  
Molecular Dynamics ◽  
Density Functional Theory ◽  
Potential Energy ◽  
Force Field ◽  
Density Functional ◽  
Energy Surface ◽  
Detonation Properties ◽  
Training Set ◽  
Functional Theory ◽  
Wide Range

<div>HN<sub>3</sub> is a unique liquid energetic material that exhibits ultrafast detonation chemistry and a transition to metallic states during detonation. We combine the ChIMES many-body reactive force field and the extended-Lagrangian multiscale shock technique (MSST) molecular dynamics method to calculate the detonation properties of HN<sub>3</sub> with the accuracy of Kohn-Sham density-functional theory. ChIMES is based on a Chebyshev polynomial expansion and can accurately reproduce density-functional theory molecular dynamics (DFT-MD) simulations for a wide range of unreactive and decomposition conditions of liquid HN<sub>3</sub>. We show that addition of random displacement configurations and the energies of gas-phase equilibrium products in the training set allows ChIMES to efficiently explore the complex potential energy surface. Schemes for selecting force field parameters and the inclusion of stress tensor and energy data in the training set are examined. Structural and dynamical properties, as well as chemistry predictions for the resulting models are benchmarked against DFT-MD. We demonstrate that the inclusion of explicit four-body energy terms is necessary to capture the potential energy surface across a wide range of conditions. The present force field, which was fit to a balance of forces, energies, and stress tensors yields excellent agreement with DFT, while exhibiting an orders-of-magnitude increase in computational efficiency over DFT-MD. Our results generally retain the accuracy of DFT-MD while yielding a high degree of computational efficiency, allowing simulations to approach orders of magnitude larger time and spatial scales. The techniques and recipes for MD model creation we present allow for direct simulation of nanosecond shock compression experiments and calculation of the detonation properties of materials with the accuracy of Kohn-Sham density-functional theory.</div>

Ab Initio Molecular Dynamics Reveals New Active Sites in Atomically Dispersed Pt1/TiO2 Catalysts

2020 ◽  
Author(s):  
Nicholas Humphrey ◽  
Selin Bac ◽  
Shaama Mallikarjun Sharada
Keyword(s):  
Molecular Dynamics ◽  
Ab Initio ◽  
Active Sites ◽  
Density Functional ◽  
Elevated Temperatures ◽  
Water Gas Shift ◽  
Ab Initio Molecular Dynamics ◽  
Catalytic Surface ◽  
Wide Range ◽  
Water Gas

<div> <div> <div> <p>We present a multi-scale modeling study of atomically dispersed Pt on the (110) surface of rutile TiO2. Using density functional theory (DFT) and ab initio molecular dynamics (AIMD), we probe the dynamic evolution of the catalytic surface at elevated temperatures. We identify metal atom diffusion as well as support atom mobility as important dynamical phenomena that enable the formation of new active sites. Among the eight new dynamically formed sites that are distinct from prior experimental and DFT reports, two sites exhibit anionic, near-linear O−Pt−O configurations. Such configurations are neither intuitive nor easily located using static methods such as DFT. Therefore, DFT alone is not sufficient to obtain a complete, dynamic description of the catalytic surface. Furthermore, the near-linear O−Pt−O sites exhibit CO binding characteristics that are markedly distinct from their parent sites, with possibly higher activity towards CO oxidation and water-gas shift reactions. Based on the wide range of adsorbate affinities exhibited by the DFT and AIMD-generated sites in this study, our aim going forward is to probe site-sensitivity of water-gas shift kinetics with these catalysts. </p> </div> </div> </div>

A comparative experimental and theoretical investigation of hydrogen-bond, halogen-bond and π–π interactions in the solid-state supramolecular assembly of 2- and 4-formylphenyl arylsulfonates

2018 ◽  
Vol 74 (7) ◽  
pp. 816-829 ◽  
Author(s):  
Hina Andleeb ◽  
Imtiaz Khan ◽  
Antonio Bauzá ◽  
Muhammad Nawaz Tahir ◽  
Jim Simpson ◽  
...  
Keyword(s):  
Solid State ◽  
Density Functional ◽  
Halogen Bond ◽  
Noncovalent Interactions ◽  
Supramolecular Assembly ◽  
Halogen Bonding ◽  
Type I ◽  
Supramolecular Architectures ◽  
Solid State Structures

To explore the operational role of noncovalent interactions in supramolecular architectures with designed topologies, a series of solid-state structures of 2- and 4-formylphenyl 4-substituted benzenesulfonates was investigated. The compounds are 2-formylphenyl 4-methylbenzenesulfonate, C14H12O4S, 3a, 2-formylphenyl 4-chlorobenzenesulfonate, C13H9ClO4S, 3b, 2-formylphenyl 4-bromobenzenesulfonate, C13H9BrO4S, 3c, 4-formylphenyl 4-methylbenzenesulfonate, C14H12O4S, 4a, 4-formylphenyl 4-chlorobenzenesulfonate, 4b, C13H9ClO4S, and 4-formylphenyl 4-bromobenzenesulfonate, C13H9BrO4S, 4c. The title compounds were synthesized under basic conditions from salicylaldehyde/4-hydroxybenzaldehydes and various aryl sulfonyl chlorides. Remarkably, halogen-bonding interactions are found to be important to rationalize the solid-state crystal structures. In particular, the formation of O...X (X = Cl and Br) and type I X...X halogen-bonding interactions have been analyzed by means of density functional theory (DFT) calculations and characterized using Bader's theory of `atoms in molecules' and molecular electrostatic potential (MEP) surfaces, confirming the relevance and stabilizing nature of these interactions. They have been compared to antiparallel π-stacking interactions that are formed between the arylsulfonates.

scholarly journals Finite-Temperature Single Molecule Vibrational Dynamics from Combined Density Functional Tight Binding Extended Lagrangian Dynamics Simulations and Time Series Analysis

2020 ◽  
Vol 20 (6) ◽  
pp. 201-212
Author(s):  
Bojana Koteska ◽  
Anastas Mishev ◽  
Ljupco Pejov
Keyword(s):  
Molecular Dynamics ◽  
Time Series ◽  
Single Molecule ◽  
Density Functional ◽  
Tight Binding ◽  
Range Data ◽  
Computationally Efficient ◽  
Vibrational Dynamics ◽  
Wide Range ◽  
Dynamics Simulations

AbstractCombining a computationally efficient and affordable molecular dynamics approach, based on atom-centered density matrix propagation scheme, with the density functional tight binding semiempirical quantum mechanics, we study the vibrational dynamics of a single molecule at series of finite temperatures, spanning quite wide range. Data generated by molecular dynamics simulations are further analyzed and processed using time series analytic methods, based on correlation functions formalism, leading to both vibrational density of states spectra and infrared absorption spectra at finite temperatures. The temperature-induced dynamics in structural intramolecular parameters is correlated to the observed changes in the spectral regions relevant to molecular detection. In particular, we consider a case when an intramolecular X-H stretching vibrational states are notably dependent on the intramolecular torsional degree of freedom, the dynamics of which is, on the other hand, strongly temperature-dependent.

scholarly journals Effect of layer charge on the crystalline swelling of Na+, K+ and Ca2+ montmorillonites: DFT and molecular dynamics studies

Clay Minerals ◽  
2016 ◽  
Vol 51 (2) ◽  
pp. 197-211 ◽  
Author(s):  
Anniina Seppälä ◽  
Eini Puhakka ◽  
Markus Olin
Keyword(s):  
Molecular Dynamics ◽  
Dft Calculations ◽  
Density Functional ◽  
Layer Charge ◽  
Swelling Properties ◽  
Crystalline Swelling ◽  
Wide Range ◽  
Molecular Dynamics Calculations ◽  
Level Information ◽  
Molecular Layers

AbstractThe swelling and cation exchange properties of montmorillonite are fundamental in a wide range of applications ranging from nanocomposites to catalytic cracking of hydrocarbons. The swelling results from several factors and, though widely studied, information on the effects of a single factor at a time is lacking. In this study, density functional theory (DFT) calculations were used to obtain atomic-level information on the swelling of montmorillonite. Molecular dynamics (MD) was used to investigate the swelling properties of montmorillonites with different layer charges and interlayer cationic compositions. Molecular dynamics calculations, with CLAYFF force field, consider three layer charges (−1.0, −0.66 and −0.5 e per unit cell) arising from octahedral substitutions and interlayer counterions of Na, K and Ca. The swelling curves obtained showed that smaller layer charge results in greater swelling but the type of the interlayer cation also has an effect. The DFT calculations were also seen to predict larger d values than MD. The formation of 1, 2 and 3 water molecular layers in the interlayer spaces was observed. Finally, the data from MD calculations were used to predict the selfdiffusion coefficients of interlayer water and cations in different montmorillonites and in general the coefficient increased with increasing water content and with decreasing layer charge.

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