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Potential energy surfaces molecular dynamics principles

Before a detailed presentation of the ab initio dynamics simulations, first the fundamental difference between atomic and molecular adsorption on the one hand and dissociative adsorption on the other hand has to be addressed. Then I will briefly discuss the question whether quantum or classical methods are appropriate for the simulation of the adsorption dynamics. This section will be followed by a short introduction into the determination of potential energy surfaces from first principles and their continuous representation by some analytical or numerical interpolation schemes. Then the dissociative adsorption and associative desorption of hydrogen at metal and semiconductor surfaces and the molecular trapping of oxygen on platinum will be discussed in some detail. [Pg.2]

Significant progress has recently been made in several areas which will have a profound effect on the ability of molecular dynamics to handle more complex problems. In this section we speculate on several areas which appear to hold promise for advancing computer modeling studies. In section 4.1, recent progress in both analytic potential energy expressions and first principles calculations are briefly mentioned. Recent advances in computational techniques are discussed in section 4.2. These include the use of constraints within the classical equations of motion to model thermostats in the surface region, and the incorporation of Monte Carlo techniques into molecular dynamics simulations. [Pg.325]

Motion of atoms in molecules can be quite well described in terms of classical mechanics, due to the relatively high mass of atomic nuclei. Given a set of starting coordinates and atomic velocities, it is possible to solve Newton s equations of motion to describe the time evolution of the atoms across the potential energy surface. In principle, such molecular dynamics (MD) simulations can give very detailed insight into chemical reactivity and some examples will be given below. [Pg.462]

In empirical force-fields calculations, the information about the electronic system is entirely contracted in the data of the ground state potential energy surface and forces acting on the nuclei. Model potentials and forces are then used to propagate the ionic dynamics, instead of performing an electronic structure calculation. This on the fly quantum calculation is the challenging part of first-principle Molecular Dynamics simulations. [Pg.230]

In this review we have shown how investigations initially of the rupture of a covalent bond have led to the study of mechanically activated reactions and the influence of mechanical force on reaction pathways and rates of reaction. The application of mechanical force to control chemistry in a precise way is still in its infancy and we anticipate more activity in this direction in the future. The use of first principles calculations in understanding the rupture process is essential as a detailed description of the electronic structure is required for the correct description of covalent bond rupture. Calculations which determine the potential energy surface for stretching a small molecule in its ground state have evolved to consider the perturbation of a the potential surface of a molecule exposed to a constant force. First principles molecular dynamics simulations have enabled the study of bond rupture and experimental parameters which affect rupture. This determined that factors such as the length of the molecule in which the bond finds itself and the rate at which the molecule is stretched affect the... [Pg.124]

In principle, classical molecular dynamics involves motion on the potential energy surface (PES). We assume that the temperature is sufficiently high to avoid problems with motion involving the lowest vibrational levels, where quantiun mechanics tends to complicate the problem. We also assume that the motion takes place on the ground state energy surface. There is no surface-crossing problem of the type that we discussed in Section 4.7. [Pg.169]

Chapter 3 treats nuclear motions on the adiabatic potential energy surfaces (PES). One of the most powerful and simplest means to study chemical dynamics is the so-called ab initio molecular dynamics (or the first principle dynamics), in which nuclear motion is described in terms of the Newtonian d3mamics on an ab initio PES. Next, we review some of the representative time-dependent quantum theory for nuclear wavepackets such as the multiconfigurational time-dependent Hartree approach. Then, we show how such nuclear wavepacket d3mamics of femtosecond time scale can be directly observed with pump>-probe photoelectron spectroscopy. [Pg.7]


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