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Chemistry

Theoretical chemistry & modeling

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Displaying 151 - 175 of 180

Thermochemistry of Ammonium Nitrate, NH4NO3, in the Gas Phase

October 7, 2010
Author(s)
Karl K. Irikura
Hildenbrand and coworkers have shown recently that the vapor above solid ammonium nitrate includes molecules of NH4NO3, not only NH3 and HNO3 as previously believed. Their measurements led to thermochemical values that imply an enthalpy change of D298 = 98

Atomistic Factors Governing Adhesion between Diamond, Amorphous Carbon, and Model Diamond Nanocomposite Surfaces

October 1, 2010
Author(s)
Pamela L. Piotrowski, Rachel J. Cannara, Guangtu Gao, Joseph J. Urban, Robert W. Carpick, Judith A. Harrison
Complementary atomic force microscopy (AFM) and molecular dynamics (MD) simulations were conducted to determine the work of adhesion for diamond(111)(1x1) and diamond(001)(2x1) surfaces paired with other carbon-based materials. In the AFM experiments, the

Kinetics of the Thermal Reaction of H Atoms with Propyne

April 15, 2010
Author(s)
Claudette M. Rosado-Reyes, Jeffrey A. Manion, Wing Tsang
The reaction of hydrogen atoms with propyne(CH≡CCH3) has been investigated in a heated single pulse shock tube at temperatures of 870-1145K and pressures of 2-9 bar. Stable products from various reaction channels (terminal and non-terminal H addition, and

Composition and concentration anomalies for structure and dynamics of Gaussian-core mixtures

August 25, 2009
Author(s)
Vincent K. Shen, Mark J. Pond, William P. Krekelberg, Jeffrey R. Errington, Thomas M. Truskett
We report molecular dynamics simulation results for two-component fluid mixtures of Gaussian-core particles, focusing on how tracer diffusivities and static pair correlations depend on temperature, particle concentration, and composition. At low particle

Scaling Factors and Uncertainties for ab Initio Anharmonic Vibrational Frequencies

August 21, 2009
Author(s)
Russell D. Johnson III, Karl K. Irikura, Raghu N. Kacker, Ruediger Kessel
To predict the vibrational spectra of molecules, ab initio calculations are often used to compute harmonic frequencies, which are usually scaled by empirical factors as an approximate correction for errors in the force constants and for anharmonic effects

The Fifth Industrial Fluid Properties Simulation Challenge

August 5, 2009
Author(s)
F Case, Anne M. Chaka, J Moore, Raymond D. Mountain, J Olson, Richard B. Ross, Martin Schiller, Vincent K. Shen, Eric A. Stahlberg
The fifth industrial fluid properties simulation challenge was held in 2008. In it the contestants were challenged to predict specific, industrially relevant, properties of fluid systems, namely the 1-octanol /water partition coefficient and the infinite

Uncertainties in Scaling Factors for ab Initio Vibrational Zero-Point Energies

March 21, 2009
Author(s)
Karl K. Irikura, Russell D. Johnson III, Raghu N. Kacker, Ruediger Kessel
Vibrational zero-point energies (ZPEs) determined from ab initio calculations are often scaled by empirical factors. An empirical scaling factor partially compensates for the effects arising from vibrational anharmonicity and incomplete treatment of

Standards and Standardization of Molecular Diagnostics

August 15, 2005
Author(s)
J P. Jakupciak, C D. O'Connell
DNA has become a major target for clinical laboratory testing over the past 5 years, and RNA testing is emerging for infectious disease and gene expression (1). To normalize laboratory results across different technology platforms as well as between

Reversible Proton Transfer Dynamics in Bacteriorhodopsin

August 20, 2004
Author(s)
Y. S. Lee, Morris Krauss
Proton transfer in bacteriorhodopsin from the cytoplasm to the extracellular side is initiated from protonated asp96 in the cytoplasmic region towards the deprotonated Schiff base. This occurs in the transition from the photocycle late M state to the N

Detection Limit of Isotope Dilution Mass Spectrometry

August 1, 2002
Author(s)
Lee L. Yu, John D. Fassett, William F. Guthrie
The detection limit is an important figure of merit for evaluating instrumentation and analytical methods. While the detection limit for techniques using linear calibration functions has been studied extensively, this fundamental metric has rarely been

Ab Initio Structure of the Active Site of Phosphotriesterase

February 1, 2001
Author(s)
Morris Krauss
This research exploits two recent developments to obtain a fundamental understanding of the metalloenzyme active site using the bi-metallic enzyme phosphotriesterase as an example of this class. First, is the theoretical prediction that the structure and

CASSCF Investigation of Electronic Excited States of 2-Aminopurine

January 11, 2001
Author(s)
E L. Rachofsky, J B. Ross, Morris Krauss, R Osman
2-aminopurine is a highly fluorescent analog of adenine that can be incorporated synthetically into DNA with little perturbation of the native double-helical structure. The sensitive dependence of the quantum yield of this fluorophore on nucleic acid

Escherynes: Belt-Shaped Carbon Allotropes

January 1, 2001
Author(s)
Ernesto Estrada, Yamil Simon
The discoveries of fullerenes, carbon nanotubes and graphene have increased dramatically the research interests on all-carbon materials. Carbon-based materials have found applications in nanotechnology, material sciences, electronics, optic and

Gradient Search Method for Orbital-Dependent Density-Functional Calculations

December 15, 2000
Author(s)
R Hyman, Mark D. Stiles, A Zangwill
We describe a gradient search method appropriate for electronic structure problems where the energy functionals are explicitly orbital-dependent. The ground state is found by minimizing the total energy with respect to the scalar and vector potentials that

Spectroscopy of 2-aminopurine: An MCSCF Study

December 1, 1998
Author(s)
E L. Rachofsky, J B. Ross, Morris Krauss, R Osman
2-aminopurine (2AP) is a highly fluorescent isomer of adenine that can be incorporated into DNA as a probe of structure, dynamics, and protein-DNA interactions. Interpretation of the fluorescence of 2AP in DNA requires a model of the electronic structure
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