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year-2002

Publications during 2002

Article Reference A Fourfold Coordinated Point Defect in Silicon
Vacancies, interstitials, and Frenkel pairs are considered to be the basic point defects in silicon. We challenge this point of view by presenting density functional calculations that show that there is a stable point defect in silicon that has fourfold coordination and is lower in energy than the traditional defects.
Article Reference A Hamiltonian electrostatic coupling scheme for hybrid Car–Parrinello molecular dynamics simulations
 
Article Reference A revised MRCI-algorithm. I. Efficient combination of spin adaptation with individual configuration selection coupled to an effective valence-shell Hamiltonian
 
Article Reference A Theoretical Study of the Interaction of HCl with Crystalline NAT
Using density-functional-plane-wave-based and localized-orbital computational methods, we systematically examine the binding of molecular HCl at a variety of surface sites on crystalline nitric acid trihydrate (NAT), a step preceding the chlorine activation reactions that contribute to the depletion of stratospheric ozone at high latitudes. We pay particular attention to the role played by surface dangling (non-hydrogen-bonding) OH groups. After optimizing six low index faces, we find that NAT(001) and (001̄) faces are thermodynamically the most stable. Only one surface site on the (001) face, with one nearby dangling OH group, exhibits a high affinity for HCl. At this binding site, adsorbed HCl forms a strong H···O hydrogen bond with an NO3- ion and a weaker Cl···H hydrogen bond with a nearby H2O molecule. The interaction energy and enthalpy at 190 K corrected for zero-point energies are 23 and 25 kJ/mol, respectively. The presence of one strong binding site per simulation cell, versus at least three previously reported on the (0001) face of ice Ih (Mantz, Y. A.; Geiger, F. M.; Molina, L. T.; Molina, M. J.; Trout, B. L. J. Phys. Chem. A 2000, 105, 7037), leads to a prediction of a lower HCl surface coverage on NAT than on ice, qualitatively consistent with experiments conducted on these surfaces. Additionally, we present kinetic and thermodynamic evidence that molecular HCl, adsorbed near one or two dangling OH groups, does not dissociate on NAT. By contrast, molecularly adsorbed HCl likely dissociates when interacting strongly with two dangling OH group on the ice Ih (0001) face as reported in previously published theoretical studies (Svanberg, M.; Pettersson, J. B. C.; Bolton, K. J. Phys. Chem. A 2000, 104, 5787; Mantz, Y. A.; Geiger, F. M.; Molina, L. T.; Molina, M. J.; Trout, B. L. Chem. Phys. Lett. 2001, 348, 285).
Article Reference Ab Initio Molecular Dynamics for Molecules with Variable Numbers of Electrons
The ab initio molecular dynamics method is extended to treat exchange of electrons between molecules and a reservoir at fixed chemical potential. The method is based on a rigorously grand-canonical density functional approach using separate potential energy surfaces for each oxidation state. It is shown that the resulting discontinuous dependency of excess charge on chemical potential is consistent with the statistical thermodynamics of equilibrium gas-phase reactions. The method is illustrated by an application to the adiabatic redox dynamics of an aniline molecule.
Article Reference Ab Initio Molecular Dynamics Investigation of the Concentration Dependence of Charged Defect Transport in Basic Solutions via Calculation of the Infrared Spectrum†
The concentration dependence of the anomalous proton transport mechanism in aqueous KOD solution is studied using ab initio molecular dynamics. A high concentration of 13 M is chosen because of the availability of Raman and infrared spectroscopic data at this concentration. Differences in certain features of these spectra have been interpreted in terms of the so-called “proton hole” picture of the proton transport mechanism in basic solutions. The proton hole mechanism asserts that the charged defect transport in basic solutions follows the same mechanism as in acidic solutions (where the charged defect is H3O+) with all of the hydrogen-bond polarities reversed. By computing the infrared spectrum directly from an ab initio molecular dynamics simulation, we are able to validate our ab initio approach against the experimental data. However, the mechanism of charged defect transport that emerges from the simulation is considerably different from the proton hole mechanism and follows that recently reported by Tuckerman, et al. (Tuckerman, M. E.; Marx, D.; Parrinello, M. Nature 2002, 417, 925). For comparison, a lower concentration, 1.5 M, is also simulated and the transport mechanism compared to the high concentration case. It is found that the mechanisms are similar; however, the mobility of both K+ and OD- is slower at high concentration, a finding that is in keeping with the fact that the molar conductivity of electrolytes decreases with increasing concentration. Other similarities and differences between the two concentrations are highlighted, and a new interpretation of the spectral data is proposed.
Article Reference Ab initio molecular dynamics simulation of the H/InP(100)–water interface
 
Article Reference Ab initio molecular dynamics with Density Functional Theory
 
Article Reference Ab-initio Study of NMR Chemical Shifts of Water Under Normal and Supercritical Conditions
 
Article Reference Ab-initio study of the electromagnetic response and polarizability properties of carbon chains
We present the most complete set of calculations to date of the ground state electronic properties and of the optical/UV response function of linear carbon chains CN, using ab-initio methods based on local density and on time-dependent local density approximations (LDA and TDLDA). Making use of the associated transition densities and wavefunctions we are able to provide microscopic insight into the collectivity of the corresponding plasmon spectrum in terms of correlated particle-hole excitations. From this analysis it is found that the (one-dimensional 1-D) delocalization of [pi] (valence) electrons is responsible for the conspicuous values of the static dipole polarizability and of the high value of the exponent describing its dependence with the number of carbon atoms. Within this framework the electronic structure and linear response function of a carbon ring is also calculated. Although many properties of this function are similar to that associated with linear chains of the same number of atoms, the corresponding polarizabilities differ appreciably, providing a reliable method to distinguish between linear and close structures. The first principle results of the properties of linear carbon chains are compared with both theoretical and experimental results available in the literature, and constitute the basis for a systematic study of these 1-D sp-bonded systems, which have been found to be involved in such seemingly disparate phenomena as fullerene growth mechanism and diffuse interstellar bands.
Article Reference An ab initio study of water molecules in the bromide ion solvation shell
 
Article Reference An Efficient Algorithm for Electronic-Structure Calculations
We show how to adapt the quasi-Newton method to the electronic-structure calculations using systematic basis sets. Our implementation requires less iterations than the conjugate gradient method, while the computational cost per iteration is much lower. The memory usage is also quite modest, thanks to the efficient representation of the approximate Hessian. ©2002 The Physical Society of Japan
Article Reference Anharmonic Raman Spectra in High-Pressure Ice from Ab Initio Simulations
We calculate from ab initio molecular dynamics the Raman scattering of high-pressure ice. To this effect we apply a new method based on the Berry phase theory of polarization. Our results are in agreement with recent and difficult experiments and are compatible with a picture in which ice VII is a proton-disordered system and in ice X the hydrogen bond is symmetric.
Article Reference Breaking Bonds by Mechanical Stress:  When Do Electrons Decide for the Other Side?
Using first-principles molecular dynamics, we have simulated reactions that can be induced by mechanical stress in a polymer. We have stretched a small piece of poly(ethylene glycol) (PEG) in water at finite temperature. Both the molecule and the solvent were described quantum mechanically on an equal level. The formation of ions was observed, which corresponds to a heterolytic bond cleavage. We were able to monitor the motion of the electrons during the reactions. Our simulations show that the electron transfer and the breaking of the bond occur almost simultaneously and that both processes are initiated by the approach of a solvent molecule toward the destabilized bond.
Article Reference Breaking Bonds by Mechanical Stress: When Do Electrons Decide for the Other Side?
 
Article Reference Car–Parrinello molecular dynamics simulation of liquid water: New results
 
Article Reference Car—Parrinello study of Ziegler—Natta heterogeneous catalysis: stability and destabilization problems of the active site models
 
Article Reference Chemisorption on small clusters: can vertical detachment energy measurements provide chemical information? H on Au as a case study
 
Article Reference Chloride Anion on Aqueous Clusters, at the Air−Water Interface, and in Liquid Water:  Solvent Effects on Cl- Polarizability
The effect of asymmetric aqueous solvation on the polarizability of the chloride anion is investigated by accurate ab initio calculations on structures obtained from classical molecular dynamics and Car−Parrinello molecular dynamics simulations. It is shown that a water environment significantly reduces the halide polarizability on clusters, at interfaces, and in the bulk. In the relatively rigid cluster environment, the amount of this reduction strongly depends on the particular geometry of the complex, while in more disordered, extended liquid systems, the geometric effect is much weaker. Therefore, a single effective value around 4 Å3 may be employed for the chloride anion polarizability in aqueous environments.
Article Reference Classical polarizable force fields parametrized from ab initio calculations
 
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