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THOR in Solid Systems

Electronic structures associated with defects, interfaces, and surfaces play a critical role in structural, electrical, and transport properties of materials. Atomic scale information on electron densities, wave functions, and spectroscopic properties is needed to understand nanometer and micron scale behavior; however, the requisite composition and geometrical data are typically lacking.

We describe a hybrid approach which makes use of Classical Molecular Dynamics (MD) and Monte Carlo (MC) simulations, coupled to Embedded Cluster Density Functional (ECDF) algorithms. In this scheme, parameterized interactomic potentials are used in MD/MC to relax the defect or interface structure, subject to constrains imposed by electron microscopy and other experimental data.

ECDF calculations are carried out at equilibrium, metastable, near-equilibrium geometries, and along transition paths. Charge and bond-order analysis, along with calculated cohesive energies, are used analyze local bonding structure, and to check and refine the input potentials.

In case of solid systems other potentials are added to THOR force field as for example Buckingham tex2html_wrap_inline453 and Morse tex2html_wrap_inline453 potentials

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A more realistic interaction potential function for describing the interaction of the atom with a surface of a solid should have a `soft' repulsive part, i.e. one that allows deeper penetration at higher energies, and with a potential well in front to represent the attractive interaction with the atoms of the solid (in the case of rare gases the attractive interaction is only the dispersion (or London) interaction but for other atoms there will be stronger, chemical interactions. In all of these cases, the Morse potential function is a reasonable qualitative description of the interaction close to the surface (it does not have the right form to describe the right long range form of the dispersion interaction).

The following flowchart represent the procedure used in the coupling between MC+ECDF approaches.

Objective

In the first part of the present project, we objective to develop a computational interface to make a coupling between the Molecular Mechanic Method (MD) and the Density Functional Theory (DVM).


next up previous
Next: THOR - Stochastic Molecular Up: e Previous: THOR in Biological Systems

Kleber Mundim
Sat Jul 19 11:13:17 CDT 1997