EMSL: Gregory Schenter's Publications

Bell RC, K Wu, MJ Iedema, GK Schenter, and JP Cowin. 2009. "The Oil-Water Interface: Mapping the Solvation Potential." Journal of the American Chemical Society 131(3):1037-1042. doi:10.1021/ja805962x Abstract Ions moving across the oil water interface are strongly impacted by the continuous changes in solvation. The solvation potential for Cs+ is directly measured as they approach the oil-water interface (“oil” = 3-methylpentane), from 0.4 to 4 nm away. The oil-water interfaces are created at 40K using molecular beam epitaxy and a softlanding ion beam, with pre-placed ions. The solvation potential slope was determined at each distance by balancing it against an increasing electrostatic potential made by increasing the number of imbedded ions at that distance, and monitoring the resulting ion motion. The potential approaches the Born model for greater than z>0.4nm, and shows the predicted reduction of the polarizability at z<0.4nm.

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.

Maerzke KA, G Murdachaew, CJ Mundy, GK Schenter, and JI Siepmann. 2009. "Self-consistent polarization density functional theory: Application to Argon." Journal of Physical Chemistry A 113(10):2075-2085. doi:10.1021/jp808767y Abstract We present a comprehensive set of results for argon, a case study in weak interactions, using the selfconsistent polarization density functional theory (SCP-DFT). With minimal parameterization, SCPDFT is found is give excellent results for the dimer interaction energy, the second virial coefficient, the liquid structure, and the lattice constant and cohesion energy of the face-centered cubic (fcc) crystal compared to both accurate theoretical and experimental benchmarks. Thus, SCP-DFT holds promise as a fast, efficient, and accurate method for performing ab initio dynamics that include additional polarization and dispersion interactions for large, complex systems involving solvation and bond breaking. 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.

Rousseau RJ, GK Schenter, JL Fulton, JC Linehan, MH Engelhard, and T Autrey. 2009. "Defining Active Catalyst Structure and Reaction Pathways from ab Initio Molecular Dynamics and Operando XAFS: Dehydrogenation of Dimethylaminoborane by Rhodium Clusters ." Journal of the American Chemical Society 131(30):10516-10524. Abstract We present the results of a detailed operando XAFS and density functional theory (DFT) based ab initio molecular dynamics (AIMD) investigation of the proposed mechanism of dehydrogenation of dimethylaminoborane (DMAB) by a homogeneous Rh4 cluster catalyst. Our AIMD simulations reveal that the previously proposed Rh structures are highly fluxional exhibiting both metal cluster and ligand isomerizations and dissociaton which can only be accounted for by a examining finite temperature ensemble as generated by AIMD. It is found that a highly fluxional species Rh4((H2BNMe2)82+ is fully compatible with operando XAFS measurements which suggest that this species may be the catalyst resting state. Based on this assignment we propose a catalytic mechanism for DMAB dehydrogenation which exhibits a maximum energy barrier of 24 kcal/mol, which is half that observed for the uncatalyzed thermal reaction. 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). PNNL is operated by Battelle for the U.S. Department of Energy.

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.

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.

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.

Eustis S, D Radisic, KH Bowen, RA Bachorz, M Haranczyk, GK Schenter, and MS Gutowski. 2008. "Electron-Driven Acid-Base Chemistry: Proton Transfer from Hydrogen Chloride to Ammonia." Science 319(5865):936-939. doi:10.1126/science.1151614 Abstract It is well established that NH3 and HCl form in isolation a hydrogen bonded complex NH3…HCl rather than an ionic salt, NH4+Cl-. This experimental and theoretical study utilized anion photoelectron spectroscopy and ab initio theory to investigate the effect of an excess electron on the hydrogen bonded complex NH3 …HCl. Our results indicate that one electron is sufficient to drive the hydrogen bonded complex to form the ionic salt. We propose a stepwise mechanism for this process involving an initial dipole-bound state, followed by the formation of a distorted Rydberg species, NH40.