EMSL: Shawn Kathmann's Publications

Crosby LD, SM Kathmann, and TL Windus. 2009. "Implementation of Dynamical Nucleation Theory with Quantum Potentials." Journal of Computational Chemistry 30(5):743-749. Abstract A method is implemented within the context of Dynamical Nucleation Theory in order to efficiently determine the ab initio water dimer evaporation rate constant. The drive for increased efficiency in a Monte Carlo methodology is established by the need to use relatively expensive quantum mechanical interaction potentials. A discussion is presented illustrating the theory, algorithm, and implementation of this method to the water dimer. Hartree-Fock and second order Møller Plesset perturbation theories along with the Dang-Chang polarizable classical potential are utilized to determine the ab initio water dimer evaporation rate constant. 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.

Hess NJ, GK Schenter, MR Hartman, LL Daemen, TE Proffen, SM Kathmann, CJ Mundy, MA Hartl, DJ Heldebrant, AC Stowe, and T Autrey. 2009. "Neutron Powder Diffraction and Molecular Simulation Study of the Structural Evolution of Ammonia Borane from 15 to 340 K." Journal of Physical Chemistry A 113(9):5723-5735. doi:10.1021/jp900839c Abstract The structural behavior of perdeuterated, 11B-enriched ammonia borane, ND311BD3, was investigated by neutron powder diffraction measurements collected over the temperature range from 15 to 340 K and by molecular dynamics simulation. In the low temperature orthorhombic phase, the progressive displacement of the borane group under the amine group was observed leading to the rotation of the B-N bond parallel to the c-axis. The structural phase transition at 225 K is marked by dramatic change in the dynamics of both the amine and borane group that is problematic to extract from the metrics provided by Rietveld analysis of the NPD data alone but is evident in the molecular dynamics simulation and other spectroscopic evidence. This study highlights the valued added by complimentary experimental approaches and coupled computational studies.

Kathmann SM, VM Parvanov, GK Schenter, AC Stowe, LL Daemen, MA Hartl, JC Linehan, NJ Hess, AJ Karkamkar, and T Autrey. 2009. "Experimental and Computational Studies on Collective Hydrogen Dynamics in Ammonia Borane: Incoherent Inelastic Neutron Scattering." Journal of Chemical Physics 130(2):article no. 024507. doi:10.1063/1.3042270 Abstract Incoherent inelastic neutron scattering can be used as a sensitive probe of the vibrational dynamics in chemical hydrogen storage materials. Thermal neutron energy loss measurements at 10K are presented and compared to the vibrational power spectrum calculated using ab initio molecular dynamics of pure and deuterated ammonia borane (NH3BH3, NH3BD3, and ND3BH3). A harmonic vibrational analysis on NH3BH3 clusters was also explored to check for consistency with experiment and the power spectrum. The measured neutron spectra and computed ab initio power spectrum compare extremely well (50 to 500 cm-1) and some assignment of modes to simple motion is possible, however, it is found that the lowest modes (below 250 cm-1) are dominated by collective motion. 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.

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.

Cho HM, WJ Shaw, VM Parvanov, GK Schenter, AJ Karkamkar, NJ Hess, CJ Mundy, SM Kathmann, JA Sears, AS Lipton, PD Ellis, and T Autrey. 2008. "Molecular Structure and Dynamics in the Low Temperature (Orthorhombic) Phase of NH3BH3." Journal of Physical Chemistry A 112(18):4277-4283. doi:10.1021/jp711696 Abstract Variable temperature 2H NMR experiments on the orthorhombic phase of selectively deuterated NH3BH3 spanning the static to fast exchange limits of the borane and amine motions are reported. New values of the electric field gradient (EFG) tensor parameters have been obtained from the static 2H spectra of Vzz = 5.509(±0.275)×1014 statvolt/cm2 and ! = 0.00±0.05 for the borane hydrogens and Vzz = 9.615(±0.481)×1014 statvolt/cm2 and ! = 0.00±0.05 for the amine hydrogens. The molecular symmetry inferred from the observation of equal EFG tensors for both the boron and amine hydrogens is in sharp contrast with the Cs symmetry derived from diffraction studies. The origin of the apparent discrepancy has been investigated using molecular dynamics methods in combination with electronic structure calculations of NMR parameters, bond lengths, and bond angles. The computation of parameters from a statistical ensemble rather than from a single set of atomic Cartesian coordinates gives values that are in close quantitative agreement with the 2H NMR electric field gradient tensor measurements and are more consistent with the molecular symmetry revealed by the NMR spectra. 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.

Hess NJ, ME Bowden, VM Parvanov, CJ Mundy, SM Kathmann, GK Schenter, and T Autrey. 2008. "Spectroscopic Studies of the Phase Transition in Ammonia Borane: Raman spectroscopy of single crystal NH3BH3 as a function of temperature from 88 to 330 K." Journal of Chemical Physics 128(3):Art. No. 034508. doi:10.1063/1.2820768 Abstract Raman spectra of single crystal ammonia borane, NH3BH3, were recorded as a function of temperature from 77 to 300 K using Raman microscopy and a variable temperature stage. The orthorhombic to orientationally disordered tetragonal phase transition at 225 K was clearly evident from the decrease in the number of vibrational modes. However some of the modes in the orthorhombic phase appeared to merge 10 to 12 K below the phase transition perhaps suggesting the presence of an intermediate phase. Factor group analysis of vibrational spectra for both orthorhombic and tetragonal phase is provided. To our knowledge this is first reported vibrational spectra in the BH and NH stretching region of single crystal NH3BH3 in the orthorhombic phase.

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, IFW Kuo, and C Mundy. 2008. "Electronic Effects on the Surface Potential at the Vapor-Liquid Interface of Water." Journal of the American Chemical Society 130(49):16556-16561. doi:10.1021/ja802851w Abstract The surface potential at the vapor-liquid interface of water is relevant to many areas of chemical physics. We present the first computation of the surface potential of water using ab initio molecular dynamics. We find that the surface potential χ = -18 mV with a maximum interfacial electric field = 8.9 × 107 V/m. A comparison is made between our quantum mechanical results and those from previous molecular simulations. We find that explicit treatment of the electronic density makes a dramatic contribution to the electric properties of the vapor-liquid interface of water. The E-field can alter interfacial reactivity and transport while the surface potential can be used to determine the “chemical” contribution to the real and electrochemical potentials for ionic transport through the vapor-liquid interface. This work was supported by the U.S. Department of Energy’s (DOE) Office of Basic Energy Sciences, Chemical Sciences program and was performed in part using the Molecular Science Computing Facility (MSCF) in the William R. Wiley Environmental Molecular Sciences Laboratory, a DOE national scientific user facility located at the Pacific Northwest National Laboratory (PNNL). Pacific Northwest National Laboratory is operated by Battelle for the US Department of Energy.

Kathmann SM, GK Schenter, and SS Xantheas. 2008. "On the Determination of Monomer Dissociation Energies of Small Water Clusters from Photoionization Experiments." Journal of Physical Chemistry A 112(9):1851-1853. doi:10.1021/jp710624r Abstract Recently, water monomer dissociation energies from neutral water clusters were estimated from the measured appearance energies resulting from vacuum ultraviolet photoionization. The monomer dissociation energies of neutral water clusters were determined via a thermodynamic cycle, which encompassed the experimentally measured appearance energies of the photoionized water clusters and the previously reported dissociation energies of protonated water clusters. A key approximation was assumed - that the relaxation energy for the process ! (H2O)n + "(H2O)n -1H+ +OH• is zero. We will show that the relaxation energies are large and thus cannot be neglected. Thus, the neutral water cluster monomer dissociation energies cannot be determined directly from the measured ionization potentials since they are themselves involved in the thermodynamic cycle. This work was supported by the Division of Chemical Sciences, Geosciences and Biosciences, Office of Basic Energy Sciences, US Department of Energy. The Pacific Northwest National Laboratory is operated by Battelle for the US Department of Energy. Computer resources were provided by the Office of Science, 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.