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year-1998

Publications during 1998

Article Reference A comparative study of O2, CO, and NO binding to iron-porphyrin
 
Article Reference Ab initio approach to the structure and dynamics of metallofullerenes
 
Article Reference Ab Initio Infrared Absorption Study of the Hydrogen-Bond Symmetrization in Ice
We computed from first principles the infrared spectrum of ice at high pressure in the molecular phases VIII and VII and in the symmetric phase X by performing Car-Parrinello molecular dynamics simulations and evaluating the electronic polarization by means of the Berry phase formulation. The theoretical spectra are in good agreement with the experimental data and let us establish an unambiguous correspondence between the infrared spectrum and the underlying structure of the three different phases of ice.
Article Reference Ab initio molecular dynamics simulation of laser melting of graphite
 
Article Reference Ab Initio Molecular Dynamics Study of the Reaction of Water with Formaldehyde in Sulfuric Acid Solution
Ab initio molecular dynamics methods have been used to study the reaction mechanism of acid-catalyzed addition of water to formaldehyde in a model system of an aqueous solution of sulfuric acid. Using the method of constraints we find that an H2O molecule can be added to formaldehyde by a controlled transfer of a catalytic proton from a hydronium ion in acid solution to the carbonyl oxygen. The formation of the CO bond between the carbonyl carbon and the water oxygen occurs at a stage midway in the proton transfer process. The process can be reversed by removing the H+ from the protonated product diol, leading to CO bond breaking at approximately the same stage of proton transfer. This suggests that the kinetics of the acid-catalyzed reaction is governed by a concerted protonation and addition.
Article Reference Adsorption of potassium and oxygen on graphite: A theoretical study
 
Article Reference Alq3: ab initio calculations of its structural and electronic properties in neutral and charged states
A detailed density functional theory study is presented for the structural and electronic properties of Alq3, one of the electroluminescent material most successfully used in organic light-emitting diodes. Both geometrical isomers are considered, and interesting discrepancies are found in their electronic behavior. Calculations are compared with available experimental data and with the results of semiempirical models as well. The effects of hole and electron injection are clarified, and trap energies for the negative charge carriers are estimated.
Article Reference Atom-resolved electronic spectra for Alq[sub 3] from theory and experiment
 
Article Reference CO Oxidation on Pt(111): An Ab Initio Density Functional Theory Study
CO oxidation on Pt(111) is studied with ab initio density functional theory. The low energy pathway and transition state for the reaction are identified. The key event is the breaking of an O-metal bond prior to the formation of a chemisorbed CO2 molecule. The pathway can be rationalized in terms of competition of the O and C atoms for bonding with the underlying surface, and the predominant energetic barrier is the strength of the O-metal bond.
Article Reference Comparing the Acidities of Microporous Aluminosilicate and Silico-Aluminophosphate Catalysts: A Combined Quantum Mechanics-Interatomic Potential Function Study
 
Article Reference COMPUTATIONAL APPROACH TO THE PHYSICAL CHEMISTRY OF FULLERENES AND THEIR DERIVATIVES
 
Article Reference Density functional study of molecular crystals: Polyethylene and a crystalline analog of bisphenol-A polycarbonate
 
Article Reference Density Functional Theory and Biomolecules: A Study of Glycine, Alanine, and Their Oligopeptides
We present density functional (DF) calculations, using a pseudopotential scheme and plane waves as basis functions, for isolated molecules of the amino acids glycine and alanine, for small oligopeptides composed of glycine and alanine, and for periodic (infinite) polyalanine helices. We calculate relative energies and geometries for the low-lying isomers of glycine and alanine and for a variety of oligopeptide geometries using various DF formulations for electron exchange and correlation (LDA, PBE, BLYP, BP). Comparison is made with other theories and experiment where possible. The free molecule equilibrium geometries agree well with the limited experimental data and with post-HartreeFock (post-HF) calculations. The inclusion of gradient-corrected (nonlocal) functionals is essential when hydrogen bonds play a role in determining relative energies. This is especially true for hydrogen bonds of the type N...HO, which appear in two isomers of glycine and alanine. We obtain the most reliable results with BLYP, but the best compromise, with a considerably smaller cutoff energy, is PBE. For the polypeptides we find that the peptide bonds in the equilibrium geometries are planar to high accuracy, with dihedral angles deviating from planarity by up to 15o. The relative energies of the low-lying isomers of alanine dipeptide agree very well with post-HF calculations. The equilibrium structure of the polyalanine alpha helix is very well reproduced by our calculations.
Article Reference Density-functional study of hydration of sodium in water clusters
 
Article Reference Density-functional theory and molecular dynamics: a new perspective for simulations of biological systems
 
Article Reference Density-Functional Theory Study of Electronic and Structural Properties of Doped Polypyrroles
Electronic and structural properties of polypyrroles oxidized by different concentrations of chlorine atoms or molecules are studied with the use of a density functional method implemented with plane waves and pseudo-potentials for the core electrons. The calculated properties are compared with those obtained for the neutral system that are in good agreement with the available experimental data. The role of the counterion in the oxidation process is studied extensively and shown to be crucial for the localization of charge and structural defects.
Article Reference First Principles Molecular Dynamics Study of Ziegler−Natta Heterogeneous Catalysis
We present a first principles study of the Ziegler−Natta MgCl2-supported polymerization of ethylene in the framework of the Car-Parrinello approach. In particular we investigate the titanium active sites on the (110) surface of the support focusing on Corradini's model and the possible alternative configurations. We find that different catalyst sites are allowed and that the relevant energetics as well as the reactivity in the alkyl chain formation process strongly depend on the local geometry. During deposition of TiCl4 and complex formation, which are energetically downhill, the dynamical approach allows us to follow the reaction pathway in an unbiased way. By means of Car−Parrinello constrained molecular dynamics we then determine the free energy profiles and estimate activation barriers in the alkene insertion processes. Furthermore a dynamical study of the insertion of a second ethylene molecule offers an interesting insight into the chain growth process and the stereochemical character of the polymer, providing a complete picture of the reaction mechanism.
Article Reference Fluctuations and Bonding in Lithium Clusters
Structures and bonding of the Li8 and Li20 clusters are investigated with path integral simulations combined with electronic structure calculations. The zero-point motion of the nuclei leads to quantum fluctuations corresponding to about 100 K thermal excitations. This destroys the distinction between long and short bonds which is a characteristic feature of the optimized static structures, but does not induce a qualitative change in the cluster structures or their electronic properties.
Article Reference Glucose in Aqueous Solution by First Principles Molecular Dynamics
We present the results of the first ab initio molecular dynamics simulations, based on the Car−Parrinello method, of glucose in water, performed to investigate structural aspects of the anomeric equilibrium in aqueous solution. The analysis of the hydrogen bonds around the crucial anomeric oxygen shows a distinct solvation behavior for the β and α anomers. While the β anomer, which is the most abundant in water, allows the water molecules to flow in a disorderly manner around its anomeric site, the α anomer tends to bind them more tightly.
Article Reference Grid-free DFT implementation of local and gradient-corrected XC functionals
 
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