Author
George L. Barnes
Other affiliations: University of Wisconsin-Madison, University of Oregon, University of Nevada, Reno ...read more
Bio: George L. Barnes is an academic researcher from Siena College. The author has contributed to research in topics: Fragmentation (mass spectrometry) & Dissociation (chemistry). The author has an hindex of 20, co-authored 46 publications receiving 949 citations. Previous affiliations of George L. Barnes include University of Wisconsin-Madison & University of Oregon.
Papers
More filters
TL;DR: The preferred sense of product molecule rotation (clockwise or counterclockwise) in a bimolecular collision system has been measured and quantum calculations on the most recently reported NO-Ar potential give good agreement with the observed oscillation patterns in the sense of rotation.
Abstract: The preferred sense of product molecule rotation (clockwise or counterclockwise) in a bimolecular collision system has been measured. Rotationally inelastic collisions of nitric oxide (NO) molecules with Ar atoms were studied by combining crossed molecular beams, circularly polarized resonant multiphoton ionization probing, and velocity-mapped ion imaging detection. The observed sense of NO product rotation varies with deflection angle and is a strong function of the NO final rotational state. The largest preferences for sense of rotation are observed at the highest kinematically allowed product rotational states; for lower rotational states, the variation with deflection angle becomes oscillatory. Quantum calculations on the most recently reported NO-Ar potential give good agreement with the observed oscillation patterns in the sense of rotation.
127 citations
TL;DR: Direct dynamics simulation studies are described for bimolecular SN2 nucleophilic substitution, unimolecular decomposition, post-transition-state dynamics, mass spectrometry experiments, and semiclassical vibrational spectra.
Abstract: In a direct dynamics simulation, the technologies of chemical dynamics and electronic structure theory are coupled so that the potential energy, gradient, and Hessian required from the simulation are obtained directly from the electronic structure theory. These simulations are extensively used to (1) interpret experimental results and understand the atomic-level dynamics of chemical reactions; (2) illustrate the ability of classical simulations to correctly interpret and predict chemical dynamics when quantum effects are expected to be unimportant; (3) obtain the correct classical dynamics predicted by an electronic structure theory; (4) determine a deeper understanding of when statistical theories are valid for predicting the mechanisms and rates of chemical reactions; and (5) discover new reaction pathways and chemical dynamics. Direct dynamics simulation studies are described for bimolecular SN2 nucleophilic substitution, unimolecular decomposition, post-transition-state dynamics, mass spectrometry experiments, and semiclassical vibrational spectra. Also included are discussions of quantum effects, the accuracy of classical chemical dynamics simulation, and the methodology of direct dynamics.
118 citations
TL;DR: The VENUS/NWChem interface is designed to link the general electronic structure program (N WChem) and classical chemical dynamics simulation program (VENUS) to perform direct dynamics simulation in which the trajectories “on the fly” with the potential and its derivatives obtained directly from electronic structure theory.
90 citations
TL;DR: A new software, called tsscds2018, has been developed to discover reaction mechanisms and solve the kinetics in a fully automated fashion and employs algorithms based on Graph Theory to find transition state geometries from accelerated semiempirical dynamics simulations carried out with MOPAC2016.
Abstract: A new software, called tsscds2018, has been developed to discover reaction mechanisms and solve the kinetics in a fully automated fashion. The program employs algorithms based on Graph Theory to find transition state (TS) geometries from accelerated semiempirical dynamics simulations carried out with MOPAC2016. Then, the TSs are connected to the corresponding minima and the reaction network is obtained. Kinetic data like populations vs time or the abundancies of each product can also be obtained with our program thanks to a Kinetic Monte Carlo routine. Highly accurate ab initio potential energy diagrams and kinetics can also be obtained using an interface with Gaussian09. The source code is available on the following site: http://forge.cesga.es/wiki/g/tsscds/HomePage © 2018 Wiley Periodicals, Inc.
61 citations
TL;DR: A model of double proton tunneling in formic acid dimer using a reaction surface Hamiltonian using a diabatic representation of reaction surface modes finds that predicting these splittings is greatly complicated by subtle mixings with the inter-dimer bend states.
Abstract: A model of double proton tunneling in formic acid dimer is developed using a reaction surface Hamiltonian. The surface includes the symmetric OH stretch plus the in-plane stretch and bend interdimer vibrations. The surface Hamiltonian is coupled to a bath of five A1g and B3g normal modes obtained at the D2h transition state structure. Eigenstates are calculated using Davidson and block-Davidson iterative methods. Strong mode specific effects are found in the tunneling splittings for the reaction surface, where splittings are enhanced upon excitation of the interdimer bend motion. The results are interpreted within the framework of a diabatic representation of reaction surface modes. The splitting patterns observed for the reaction surface eigenstates are only slightly modified upon coupling to the bath states. Splitting patterns for the bath states are also determined. It is found that predicting these splittings is greatly complicated by subtle mixings with the inter-dimer bend states.
55 citations
Cited by
More filters
TL;DR: This review focuses on the NA-MQC dynamics methods and programs developed in the last 10 years, and stresses the relations between approaches and their domains of application.
Abstract: Nonadiabatic mixed quantum–classical (NA-MQC) dynamics methods form a class of computational theoretical approaches in quantum chemistry tailored to investigate the time evolution of nonadiabatic phenomena in molecules and supramolecular assemblies. NA-MQC is characterized by a partition of the molecular system into two subsystems: one to be treated quantum mechanically (usually but not restricted to electrons) and another to be dealt with classically (nuclei). The two subsystems are connected through nonadiabatic couplings terms to enforce self-consistency. A local approximation underlies the classical subsystem, implying that direct dynamics can be simulated, without needing precomputed potential energy surfaces. The NA-MQC split allows reducing computational costs, enabling the treatment of realistic molecular systems in diverse fields. Starting from the three most well-established methods—mean-field Ehrenfest, trajectory surface hopping, and multiple spawning—this review focuses on the NA-MQC dynamics...
396 citations
Pacific Northwest National Laboratory1, Lawrence Berkeley National Laboratory2, National Center for Computational Sciences3, Brookhaven National Laboratory4, Argonne National Laboratory5, Intel6, University of Texas at Arlington7, State University of New York System8, Pennsylvania State University9, Oak Ridge National Laboratory10, Washington University in St. Louis11, Wellesley College12, Maria Curie-Skłodowska University13, Iowa State University14, Academy of Sciences of the Czech Republic15, University of Tennessee at Martin16, Université libre de Bruxelles17, Facebook18, Russian Academy of Sciences19, University of Minnesota20, University of Washington21, United States Naval Research Laboratory22, Georgia Institute of Technology23, University of St Andrews24, Universidad Autónoma Metropolitana25, University of California, San Diego26, Saarland University27, Sandia National Laboratories28, University of Illinois at Urbana–Champaign29, University of Iceland30, Australian National University31, Florida Institute of Technology32, University of Science and Technology of China33, Oswaldo Cruz Foundation34, Cardiff University35, Louisiana State University36, Chinese Academy of Sciences37, National Autonomous University of Mexico38, University of Florida39, Los Alamos National Laboratory40, University of Oviedo41, Prince of Songkla University42, Ames Laboratory43, University of Utah44, Northwestern University45, Universal Display Corporation46, Federal University of Pernambuco47, CD-adapco48, Cray49, Massachusetts Institute of Technology50, Nvidia51, University of Tennessee52, Shandong Normal University53, University of Cambridge54, Advanced Micro Devices55, Technische Universität München56, Stanford University57, Wuhan University of Technology58, Stony Brook University59
TL;DR: The NWChem computational chemistry suite is reviewed, including its history, design principles, parallel tools, current capabilities, outreach, and outlook.
Abstract: Specialized computational chemistry packages have permanently reshaped the landscape of chemical and materials science by providing tools to support and guide experimental efforts and for the prediction of atomistic and electronic properties. In this regard, electronic structure packages have played a special role by using first-principle-driven methodologies to model complex chemical and materials processes. Over the past few decades, the rapid development of computing technologies and the tremendous increase in computational power have offered a unique chance to study complex transformations using sophisticated and predictive many-body techniques that describe correlated behavior of electrons in molecular and condensed phase systems at different levels of theory. In enabling these simulations, novel parallel algorithms have been able to take advantage of computational resources to address the polynomial scaling of electronic structure methods. In this paper, we briefly review the NWChem computational chemistry suite, including its history, design principles, parallel tools, current capabilities, outreach, and outlook.
342 citations
TL;DR: The NWChem computational chemistry suite as discussed by the authors provides tools to support and guide experimental efforts and for the prediction of atomistic and electronic properties by using first-principledriven methodologies to model complex chemical and materials processes.
Abstract: Specialized computational chemistry packages have permanently reshaped the landscape of chemical and materials science by providing tools to support and guide experimental efforts and for the prediction of atomistic and electronic properties. In this regard, electronic structure packages have played a special role by using first-principledriven methodologies to model complex chemical and materials processes. Over the last few decades, the rapid development of computing technologies and the tremendous increase in computational power have offered a unique chance to study complex transformations using sophisticated and predictive many-body techniques that describe correlated behavior of electrons in molecular and condensed phase systems at different levels of theory. In enabling these simulations, novel parallel algorithms have been able to take advantage of computational resources to address the polynomial scaling of electronic structure methods. In this paper, we briefly review the NWChem computational chemistry suite, including its history, design principles, parallel tools, current capabilities, outreach and outlook.
314 citations
TL;DR: Nuclear spin order may be stored in a liquid for a much longer time than the longitudinal relaxation time T1, by using rf fields to isolate states of different symmetry.
Abstract: Nuclear spin order may be stored in a liquid for a much longer time than the longitudinal relaxation time T1, by using rf fields to isolate states of different symmetry The method is demonstrated on a sample containing AX spin systems
302 citations