EMSL: Bruce C Garrett's Publications

Arseneau DJ, DG Fleming, O Sukhorukov, JH Brewer, BC Garrett, and DG Truhlar. 2009. "The muonic He atom and a preliminary study of the He-4 mu + H-2 reaction ." Physica B Condensed Matter 404(5-7):946-949. Abstract The muonic atom 4Heu has the composition a++u-e-, and is formed by stopping negative muons in He doped with a small amount of NH3 (or Xe). It may be regarded as a unique heavy H-atom isotope with a mass of 4.1 amu. As such, the study of its chemical reaction rates and comparison with those of the well-known light Mu atom (0.113amu) allows unprecedented tests of kinetic isotope effects over a range of 36 in mass. As a first example, and one which is of most fundamental interest, we have begun kinetics studies of the Heu + H2 - HeuH + H reaction in the gas phase. The first measurements, at 295K, give a rate constant of kHei = 4:1 - 0:7 x 10-16 cm3 molec-1 s-1. In comparison, variational transition state calculations give a value of 2:46 x 10-16 cm3 molec-1 s-1, some what below the measurement, despite the large error bar, raising the possibility that the calculations, on a nessentially exact potential energy surface, have underestimated the amount of quantum tunneling involved, even for this heavyH-atom isotope.

Kathmann SM, GK Schenter, BC Garrett, B Chen, and JI Siepmann. 2009. "Thermodynamics and Kinetics of Nanoclusters Controlling Gas-to-Particle Nucleation." Journal of Physical Chemistry C 113(24):10354-10370. Abstract Nucleation of new particles from vapor-phase molecular precursors is an important process in the synthesis of nanomaterials and in the formation of aerosols in the atmosphere. Vapor-to-particle nucleation is a macroscopic process controlled by nanoscale particles (e.g., molecular clusters). Computational approaches to nucleation have been limited by the lack of a consistent theory of the process and by the lack of efficient approaches to simulate the properties of clusters relevant to nucleation. In this article, we focus on two advances that allow nucleation to be treated in a rigorous manner for molecular systems: Dynamical Nucleation Theory permits a consistent treatment of the nucleation kinetics and aggregation-volume-bias Monte Carlo simulations using self-adaptive umbrella sampling combined with histogram reweighting provides an efficient approach to evaluate the thermodynamics of molecular clusters important in nucleation. The combination of these two approaches positions molecular computational approaches to make significant advances in our understanding of the mechanisms of nucleation, particularly in multiple component systems that play crucial roles in nanoscience applications and in the atmosphere. This work was supported by the U.S. Department of Energy's (DOE) Office of Basic Energy Sciences, Chemical Sciences program. The Pacific Northwest National Laboratory is operated by Battelle for DOE.

Mielke SL, D Schwenke, GC Schatz, BC Garrett, and KA Peterson. 2009. "Functional Representation for the Born-Oppenheimer Diagonal Correction and Born-Huang Adiabatic Potential Energy Surfaces for Isotopomers of H3." Journal of Physical Chemistry A 113(16):4479-4488. Abstract Multireference configuration interaction (MRCI) calculations of the Born-Oppenheimer diagonal correction (BODC) for H3 were performed at 1397 symmetry-unique configurations using the Born-Handy approach; isotopic substitution leads to 4041 symmetry-unique configurations for the DH2 mass combination. These results were then fit to a functional form that permits calculation of the BODC for any combination of isotopes. Mean unsigned fitting errors on a test grid of configurations not included in the fitting process were 0.14, 0.12, and 0.65 cm−1 for the H3, DH2, and MuH2 isotopomers, respectively. This representation can be combined with any Born-Oppenheimer potential energy surface (PES) to yield Born-Huang (BH) PESs; herein we choose the CCI potential energy surface, the uncertainties of which (~0.01 kcal/mol) are much smaller than the magnitude of the BODC. FORTRAN routines to evaluate these BH surfaces are provided. Variational transition state theory calculations are presented comparing thermal rate constants for reactions on the BO and BH surfaces to provide an initial estimate of the significance of the diagonal correction for the dynamics.

Valiev M, R D'Auria, DJ Tobias, and BC Garrett. 2009. "Interactions of Cl- and OH Radical in Aqueous Solution." Journal of Physical Chemistry A 113(31):8823-8825. Abstract Fundamental understanding of ion-radical interactions in aqueous solutions is of significant relevance to many environmentally important applications. An important example can be found in the problem involving the excess production of molecular chlorine in marine layer, where interactions between OH radical and Cl- species have been implicated as the main reason for the unexpectedly high concentration of Cl2. Current understanding of this process is hindered due to uncertainty regarding the nature of the [OHCl]- complex in aqueous phase.

Chang DT, GK Schenter, and BC Garrett. 2008. "Self-consistent polarization neglect of diatomic differential overlap: Application to water clusters." Journal of Chemical Physics 128(16):119-137 (Art. no. 164111). doi:10.1063/1.2905230 Abstract Semiempirical SCF methods such as MNDO, AM1, and PM3 have the ability to treat the formation and breaking of chemical bonds but have been found to poorly describe hydrogen bonding and weak electrostatic complexes. In contrast, most empirical potentials are not able to describe bond-breaking and formation, but have the ability to add missing elements of hydrogen bonding using classical electrostatic interactions. We present a new method which combines aspects of both NDDO-based SCF techniques and classical descriptions of polarization to describe the diffuse nature of the electronic wavefunction in a self-consistent manner. We develop the “self-consistent polarization neglect of differential diatomic overlap” (SCP-NDDO) theory with the additional description of molecular dispersion developed as a second-order perturbation theory expression. The current study seeks to model water-water interactions as a test case. To this end, we have parameterized the SCP-NDDO model to the accurate MP2/CBS estimates of small water cluster binding energies of Xantheas et al.[S. S. Xantheas, C. J. Burnham, and R. J. Harrison, J. Chem. Phys. 116, 1493 (2002); S. S. Xantheas and E. Aprà, J. Chem. Phys. 120, 823 (2004)]. Overall agreement with the ab initio binding energies (n = 2 – 6, 8) is achieved with an RMS error of 0.20 kcal/mol. We achieve noticeable improvements in the structure, vibrational frequencies, and energetic predictions of water clusters (n ≤ 21) relative to standard NDDO-based methods.

Du S, JS Francisco, GK Schenter, and BC Garrett. 2008. "Many-Body Decomposition of the Binding Energies for OH•(H2O)2 and OH•(H2O)3 Complexes." Journal of Chemical Physics 128(8):Art. No. 084307. doi:10.1063/1.2828522 Abstract We use ab initio electronic structure methods to calculate the many-body decomposition of the binding energies of the OH(H2O)n (n=2,3) complexes. We employ MP2 and CCSD(T) levels of theory with aug-cc-pVDZ and aug-cc-pVTZ basis sets and analyze the significance of the non-pairwise interactions between OH radical and the surrounding water molecules. We also evaluate the accuracy of our newly developed potential function, the modified Thole-type model (mTTM), for predicting the many-body terms in these complexes. Our analysis of the many-body contributions to the OH(H2O)n binding energies clearly shows that they are just as important in the OH interactions with water as they are for interactions in pure water systems. This work was supported by the Division of Chemical Sciences, Office of Basic Energy Sciences of the U.S. Department of Energy (DOE) and was performed in part using the Molecular Science Computing Facility in the William R. Wiley Environmental Molecular Sciences Laboratory (EMSL) at the Pacific Northwest National Laboratory. The EMSL is funded by the DOE Office of Biological and Environmental Research. Battelle operates Pacific Northwest National Laboratory for DOE. The authors thank Sotiris Xantheas, Jun Li, Tzvetelin Iordanov, and Jun Cui for helpful discussions and assistance.

Kathmann SM, BJ Palmer, GK Schenter, and BC Garrett. 2008. "Activation Energies and Potentials of Mean Force for Water Cluster Evaporation." Journal of Chemical Physics 128(6):Art. No. 064306. doi:10.1063/1.2837282 Abstract Activation energies for water cluster evaporation are of interest in many areas of chemical physics. We present the first computation of activation energies for small waters clusters using the formalism of Dynamical Nucleation Theory (DNT). To this end, individual evaporation rate constants are computed for water clusters (H2O)i, where i = 2 to 10 for temperatures ranging from 243 to 333K. These calculations employ a parallel sampling technique utilizing the Global Arrays Toolkit developed at PNNL. The resulting evaporation rate constants for each cluster are then fit to Arrhenius equations to obtain activation energies. We discuss DNT evaporation rate constants and their relation to potentials of mean force, activation energies, and how to account for non-separability of the reaction coordinate in the reactant state partition function. This work was supported by the PNNL Computational Science and Engineering LDRD Program and the Chemical and Material Sciences Division, Office of Basic Energy Sciences, Department of Energy. The Pacific Northwest National Laboratory is operated by Battelle for the US Department of Energy.

Kathmann SM, GK Schenter, and BC Garrett. 2008. "The Impact of Molecular Interactions on Atmospheric Aerosol Radiative Forcing." Advances in Quantum Chemistry 55:429-447. doi:10.1016/S0065-3276(07)00220-1 Abstract We review the chemical physics of nucleation and its connection to atmospheric aerosol radiative forcing. The scientific community has demanded a comprehensive investigation of aerosol radiative forcing of climate. Particular emphasis has been placed on gaining the fundamental knowledge necessary to accurately predict aerosol formation and growth and their subsequent radiative affects on climate. The chemical physics of the molecular clusters underlying nucleation will be outlined and future developments towards modeling multi-component nucleation in the atmosphere discussed. This work was supported by the Division of Chemical Sciences, Office of Basic Energy Sciences of the U.S. Department of Energy (DOE) and calculations were performed in part using the Molecular Science Computing Facility in the William R. Wiley Environmental Molecular Sciences Laboratory (EMSL) at the Pacific Northwest National Laboratory. The EMSL is funded by the DOE Office of Biological and Environmental Research. Battelle operates Pacific Northwest National Laboratory for DOE.

Morita A, and BC Garrett. 2008. "Molecular Theory of Mass Transfer Kinetics and Dynamics at Gas/Water Interface." Fluid Dynamics Research 40(7-8):459-473. Abstract The mass transfer mechanism across gas/water interface is studied with molecu- lar dynamics (MD) simulation. The MD results provide a robust and qualitatively consistent picture to previous studies about microscopic aspects of mass transfer, including interface structure, free energy profiles for the uptake, scattering dynamics and energy relaxation of impinging molecules. These MD results are quantitatively compared with experimental uptake measurements, and we found that apparent inconsistency between MD and experiment could be partly resolved by precise de- composition of the observed kinetics into elemental steps. Remaining issues and future perspectives toward constructing a comprehensive mutli-scale description of interfacial mass transfer are summarized.

Du S, JS Francisco, GK Schenter, and BC Garrett. 2007. "Ab initio and analytical intermolecular potential for ClO-H2O." Journal of Chemical Physics 126(11):146-155. doi:10.1063/1.2566537 Abstract In recent years, the ClO free radical has been found to play an important role in the ozone removal processes in the atmosphere. In this work, we present a Potential Energy Surface (PES) Scan of the ClO•H2O system with high-level ab initio methods. Because of the existence of low-lying excited states of the ClO•H2O complex, and their potential impact on the chemical behavior of the ClO radical in the atmosphere, we perform a PES scan at CCSD(T)/aug-cc-pVTZ level of both the first excited and ground states in order to model the physics of the unpaired electron in the ClO radical. Analytical potentials for both ground and excited states, with internal molecular coordinates held fixed, were built based on a Thole Type Model. The two minima of the ClO•H2O complex are recovered by the analytical potential. This work was supported by the Office of Basic Energy Sciences of the Department of Energy, in part by the Chemical Sciences program and in part by the Engineering and Geosciences Division. The Pacific Northwest National Laboratory is operated by Battelle for the U.S. Department of Energy.