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Research Interests: Engineering, Genetics, Chemistry, Computational Chemistry, Quantum Mechanics, and 13 moreQuantum, Physical sciences, Hydrogen Bond, CHEMICAL SCIENCES, Second Order, Biological systems, Ab Initio, Empirical Method, Ab Initio Calculation, Force Field Analysis, Perturbation Theory, Nucleic Acid, and Morse potential
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Research Interests: Computer Science, Chemistry, Analytical Chemistry, Nonlinear Optics, Quantum Mechanics, and 15 moreSocial Media, Icon, Band Gap, Optical Properties, Citation, CHEMICAL SCIENCES, Mathematical Model, Charge Transport, ICON, Charge transfer, Absorption Spectra, Physical Properties, Molecular Structure, The American, and Dipole Moment
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The mechanism for the formation of hexamethylenetetraamine predicts the formation of aminomethanol from the addition of ammonia to formaldehyde. This molecule subsequently undergoes unimolecular decomposition to form methanimine and... more
The mechanism for the formation of hexamethylenetetraamine predicts the formation of aminomethanol from the addition of ammonia to formaldehyde. This molecule subsequently undergoes unimolecular decomposition to form methanimine and water. Aminomethanol is the predicted precursor to interstellar glycine, and is therefore of great interest for laboratory spectroscopic study, which would serve as the basis for observational searches. The height of the water loss barrier is therefore useful in the determination of an appropriate experimental approach for spectroscopic characterization of aminomethanol. We have determined the height of this barrier to be 55kcal∕mol at ambient temperatures. In addition, we have determined the infinite-pressure Rice–Ramsperger–Kassel–Marcus unimolecular decomposition rate to be <10−25s−1 at 300K, indicating gas-phase kinetic stability for typical laboratory and hot core temperatures. Therefore, spectroscopic characterization of and observational search...
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Starburst‐Dendrimere sind dreidimensionale, hoch geordnete oligomere und polymere Verbindungen, die ausgehend von kleinen Molekülen – „Initiatorkernen”︁ wie Ammoniak oder Pentaerythrit – durch eine sich ständig wiederholende... more
Starburst‐Dendrimere sind dreidimensionale, hoch geordnete oligomere und polymere Verbindungen, die ausgehend von kleinen Molekülen – „Initiatorkernen”︁ wie Ammoniak oder Pentaerythrit – durch eine sich ständig wiederholende Reaktionsfolge entstehen. Bei den Synthesen, bei denen Schutzgruppentechniken von entscheidender Bedeutung sind, werden diskrete Entwicklungsstufen – „Generationen”︁ – durchlaufen, deren Größe, Gestalt und Oberflächenchemie durch die Aufbauschritte und die Synthesebausteine kontrolliert werden können. Mit den Starburst‐Dendrimeren und verwandten Verbindungen können einige Eigenschaften von Micellen und Liposomen nachgeahmt werden, aber auch solche von Biomakromolekülen und noch komplizierteren aber gleichfalls hoch geordneten Bausteinen biologischer Systeme. Vielerlei Anwendungen dieser neuen Verbindungsklasse sind denkbar, insbesondere im Bereich der Nachahmung großer Biomoleküle (Arzneimitteltransport, Impfstoffe). Dieser neue Zweig der „Supramolekularen Chemi...
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Research Interests: Chemistry, Kinetics, Surface Chemistry, Molecular Dynamics, Molecular Simulation, and 12 moreHydrocarbon, Physical sciences, Methane, CHEMICAL SCIENCES, Linear Quadratic regulator, Structural Similarity Index, Force Field Analysis, Finite Temperature, Molecular Dynamic Simulation, Structural similarity, Transferability, and Molecular dynamic
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Research Interests: Physics, Quantum Mechanics, Solvation, Icon, The, and 4 moreCitation, CHEMICAL SCIENCES, ICON, and Charge Distribution
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We use first-principles quantum mechanical calculations to study diamond thin film growth on the (100) surface using CCl radicals as the carbon source. Our results show that CCl inserts into the surface dimer C-C bonds with a barrier of... more
We use first-principles quantum mechanical calculations to study diamond thin film growth on the (100) surface using CCl radicals as the carbon source. Our results show that CCl inserts into the surface dimer C-C bonds with a barrier of 10.5 kcal/mol, roughly half of the energy required for traditional CH2 insertion (22.0 kcal/mol). In addition to this, CCl has improved surface mobility (∼30.0 kcal/mol barrier, versus 35 kcal/mol for CH2, along the C-C dimer chain direction), and hydrogen abstraction from the surface is also favored via atomic Cl in the vapor phase. These results explain the lower substrate temperatures achieved in crystal diamond growth from the use of chlorinated sources in CVD processes, as opposed to the more traditional CH4/H2 derived species. Our results also suggest that further reductions in substrate temperatures are possible from using CCl as the only carbon source.
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We have investigated the efficacy of ab initio effective potentials in replacing the core electrons of atoms for use in molecular calculations. The effective potentials are obtained from ab initio GI calculations on atoms and are unique... more
We have investigated the efficacy of ab initio effective potentials in replacing the core electrons of atoms for use in molecular calculations. The effective potentials are obtained from ab initio GI calculations on atoms and are unique and local. We find that the use of these effective potentials to replace the core orbitals of such molecules as LiH, Li2, BH, or LiH2, leads to wavefunctions in excellent agreement with all-electron ab initio results. The use of such effective potentials should allow ab initio quality wave-functions to be obtained for systems too large for the ab initio consideration of all the electrons.
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The effect of basis set and electron correlation on the singlet–triplet splitting (ΔEST) of CH2 is examined using the generalized valence bond (GVB) approach. For a standard double zeta plus polarization basis, the GVB based calculation... more
The effect of basis set and electron correlation on the singlet–triplet splitting (ΔEST) of CH2 is examined using the generalized valence bond (GVB) approach. For a standard double zeta plus polarization basis, the GVB based calculation (with only 20–25 spin eigenfunctions) approaches the full CI result (∼220 000 spin eigenfunctions) of Bauschlicher and Taylor to within 0.5 kcal/mol for this basis, but both differ substantially from experiment (errors of 2.4 and 2.9 kcal/mol for GVB and full CI, respectively). We have studied the convergence of ΔEST with basis set and find that an extremely extended basis (triple zeta sp, diffuse sp, triple zeta d, double zeta f ) for GVB yields ΔEST=9.03 kcal/mol, in excellent agreement with the experimental value of 9.09±0.20 kcal/mol.
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We derive an analytical expression of the second virial coefficient of d-dimensional hard sphere fluids confined to slit pores by applying Speedy and Reiss’ interpretation of cavity space. We confirm that this coefficient is identical to... more
We derive an analytical expression of the second virial coefficient of d-dimensional hard sphere fluids confined to slit pores by applying Speedy and Reiss’ interpretation of cavity space. We confirm that this coefficient is identical to the one obtained from the Mayer cluster expansion up to second order with respect to fugacity. The key step of both approaches is to evaluate either the surface area or the volume of the d-dimensional exclusion sphere confined to a slit pore. We, further, present an analytical form of thermodynamic functions such as entropy and pressure tensor as a function of the size of the slit pore. Molecular dynamics simulations are performed for d = 2 and d = 3, and the results are compared with analytically obtained equations of state. They agree satisfactorily in the low density regime, and, for given density, the agreement of the results becomes excellent as the width of the slit pore gets smaller, because the higher order virial coefficients become unimpor...
Research Interests: Engineering, Thermodynamics, Chemistry, Chemical Physics, Medicine, and 15 moreHigher Order Thinking, Computer Simulation, Phase equilibria, Physical sciences, CHEMICAL SCIENCES, Learning Theory and Modeling, Second Order, Surface Area, Molecular Dynamic Simulation, Thermodynamic Properties, Virial Expansion, Cluster Expansion, Equation of State, Higher order, and Low density
We studied melting and freezing of Ni nanoclusters with up to 8007 atoms (5.7 nm) using molecular dynamics with the quantum-Sutten–Chen many-body force field. We find a transition from cluster or molecular behavior below ∼500 atoms to a... more
We studied melting and freezing of Ni nanoclusters with up to 8007 atoms (5.7 nm) using molecular dynamics with the quantum-Sutten–Chen many-body force field. We find a transition from cluster or molecular behavior below ∼500 atoms to a mesoscale nanocrystal regime (well-defined bulk and surface properties) above ∼750 atoms (2.7 nm). We find that the mesoscale nanocrystals melt via surface processes, leading to Tm,N=Tm,bulk−αN−1/3, dropping from Tm,bulk=1760 K to Tm,336=980 K. Cooling from the melt leads first to supercooled clusters with icosahedral local structure. For N>400 the supercooled clusters transform to FCC grains, but smaller values of N lead to a glassy structure with substantial icosahedral character.
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Abstract A technique for solving the Hartree-Fock equations is proposed which has the property that the virtual orbitals from the ground state wavefunction are variationally correct approximations to the self-consistent orbitals for the... more
Abstract A technique for solving the Hartree-Fock equations is proposed which has the property that the virtual orbitals from the ground state wavefunction are variationally correct approximations to the self-consistent orbitals for the excited states. This allows a whole series of excited wavefunctions to be obtained from one calculation. This method was applied to a number of low-lying singlet and triplet excited states of H2O, and found to lead to good results.
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Starburst dendrimers are three‐dimensional, highly ordered oligomeric and polymeric compounds formed by reiterative reaction sequences starting from smaller molecules—“initiator cores” such as ammonia or pentaerythritol. Protecting group... more
Starburst dendrimers are three‐dimensional, highly ordered oligomeric and polymeric compounds formed by reiterative reaction sequences starting from smaller molecules—“initiator cores” such as ammonia or pentaerythritol. Protecting group strategies are crucial in these syntheses, which proceed via discrete “Aufbau” stages referred to as generations. Critical molecular design parameters (CMDPs) such as size, shape, and surface chemistry may be controlled by the reactions and synthetic building blocks used. Starburst dendrimers can mimic certain properties of micelles and liposomes and even those of biomolecules and the still more complicated, but highly organized, building blocks of biological systems. Numerous applications of these compounds are conceivable, particularly in mimicking the functions of large biomolecules as drug carriers and immunogens. This new branch of “supramolecular chemistry” should spark new developments in both organic and macromolecular chemistry.
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Page 1. 368 Goddard et al. Accounts of Chemical Research Generalized Valence Bond Description of Bonding in Low-Lying States of Molecules William A. Goddard III,*la Thom H. Dunning, Jr., William J. Hunt, and P. Jeffrey Hay ...
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Design of durable solar CO2 conversion devices requires a mechanistic understanding of molecular-level reactions at the electrode-electrolyte interface that lead to interfacial degradation.[1] This interface often incorporates such... more
Design of durable solar CO2 conversion devices requires a mechanistic understanding of molecular-level reactions at the electrode-electrolyte interface that lead to interfacial degradation.[1] This interface often incorporates such features as a porous and rough surface to maximize active area and enhance catalytic performance. However, this roughness may introduce local water pool inclusions, whose size may have an unforeseen, detrimental impact on device durability due to their local pH being very different from the bulk pH. It is well-recognized that for water pools containing less than molecules, the solution pH cannot be defined in the conventional sense because the pools are too small to support stable water ion concentrations near neutral pH. Rather, the water ion concentrations fluctuate to very high values for short periods of time. To better understand pH in small pools, we combine theoretical calculations using QM/MD and stochastic simulations [3]. We combined Ab initio M...
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Glassy polymers are often used for gas separations because of their high selectivity. Although the dual‐mode permeation model correctly fits their sorption and permeation isotherms, its physical interpretation is disputed, and it does not... more
Glassy polymers are often used for gas separations because of their high selectivity. Although the dual‐mode permeation model correctly fits their sorption and permeation isotherms, its physical interpretation is disputed, and it does not describe permeation far from steady state, a condition expected when separations involve intermittent renewable energy sources. To develop a more comprehensive permeation model, we combine experiment, molecular dynamics, and multiscale reaction–diffusion modeling to characterize the time‐dependent permeation of N2 and CO2 through a glassy poly(dimethyl phenylene oxide) membrane, a model system. Simulations of experimental time‐dependent permeation data for both gases in the presteady‐state and steady‐state regimes show that both single‐ and dual‐mode reaction–diffusion models reproduce the experimental observations, and that sorbed gas concentrations lag the external pressure rise. The results point to environment‐sensitive diffusion coefficients a...