Ab initio method Method solely based on the laws of quantum mechanics—the first principles referred to the name ab initio—and on the values of a small number of physical constants.

AM1 simulations Semiempirical electronic structure method. The full name is Austin Model 1, similar to MNDO (modified intermediate neglect of differential overlap), based upon NDDO (neglect of diatomic differential overlap).

Buckminsterfullerene Broad term covering the variety of buckyballs and carbon nanotube structures. Named after the architect Buckminster Fuller, who is famous for the geodesic dome, which buckyballs resemble.

Capillarity General term for phenomena observed in liquids due to intermolecular attraction at the liquid boundary, for example, the rise or depression of liquids in narrow tubes, the formation of films, drops, bubbles, and so on. Compressed hydrogen storage Hydrogen storage pressure (typically some 20 MPa).

Density functional theory In parallel to the development of ab initio theory, it was theorized that all molecular properties could be described as a function of the electron density (Hohenberg and Kohn, 1964). Density function theory is a theoretical approach to describe the electron density by using mathematical functions, called functionals. Electronic structure method Uses the laws of quantum mechanics rather than classical physics as the basis for their computation. Quantum mechanics states that the energy and other related properties of a molecule may be obtained by solving the Schrodinger equation (Hft = Eft, where H is the Hamiltonian operator, E is the energy of the particle, and ft is the wavefunction). There are now three major classes of electronic structure methods: semiempirical method, ab initio method, and density functional method. Fuel cell Electrochemical device that continuously converts the chemical energy of a fuel to electrical energy. Hydrogen economy Such an economy is one where hydrogen is used for energy storage, distribution, and utilization.

Inelastic neutron scattering (INS) Process of scattering neutrons from a specimen, accompanied by a change in energy of the neutron. Neutron beams for INS may be produced by nuclear reactors or by spallation reactions induced by accelerating charged particles into an appropriate target. After moderation, a monochromatic neutron beam can be extracted either using crystal monochromators or via time-of-flight methods.

Lennard-Jones potential Mathematical form of the potential-energy curve that describes the interaction of molecules, which stems from the work of the English chemist J.E. Lennard-Jones.

Metal hydride storage Storage of hydrogen by use of a metal alloy. The hydrogen is soaked into the alloy like into a sponge, and fills the spaces in the crystal lattice of the alloy. The storage is filled, applying a modest overpressure, and is usually operated in the temperature range of 20-80 °C. Molecular dynamics Simulation of the time-dependent behavior of a molecular system, such as vibrational motion or Brownian motion. It requires a way to compute the energy of the system, most often using a molecular mechanics calculation. This energy expression is used to compute the forces on the atom for any given geometry. Molecular mechanics method Uses the laws of classical physics to predict the structures and properties of molecules. M0ller-Plesset (MP) calculation This was theorized that the electron correlation was a perturbation of the wavefunc-tion, and so the MP perturbation theory could be applied to the HF (Hartree-Fock) wavefunction to include the electron correlation. As more perturbations are made to the system, more electron correlation is included; these methods are denoted as MP2, MP3, and MP4.

Monte Carlo methods There are many types of calculations that are referred to as Monte Carlo calculations. All Monte Carlo methods are built around some sort of a random sampling, which is simulated with a random-number-generating algorithm. In computational chemistry, a Monte Carlo simulation is usually one in which the location, orientation, and perhaps geometry of a molecule or collection of molecules are chosen according to a statistical distribution. MWNT Multiwalled carbon nanotube. ONIOM approach The full name is "our own n-layered integrated molecule orbital and molecular mechanics" developed by Svensson et al. at Emory University, USA, in 1996. This method allows the accuracy of quantum mechanics and the large molecule capability of molecular mechanics methods to be combined. The method works by dividing a molecular system into successively smaller domains that can each be treated at increasingly sophisticated theory levels. Semiempirical method Uses parameters derived from experimental data to simplify the computation. It solves an approximate form of the Schrodinger equation that depends on having appropriate parameters available for the type of chemical system under investigation.

Statistical mechanics methods Statistical mechanics is the mathematical means to calculate the thermodynamic properties of bulk materials from a molecular description of the materials. Statistical mechanics computations are often tacked onto the end of ab initio vibrational frequency calculations for gas-phase properties at low pressure. For condensed-phase properties, often molecular dynamics or Monte Carlo calculations are necessary in order to obtain statistical data.

SWNT Single-walled carbon nanotube.

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