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【分享】三类分子动力学
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Classical Molecular Dynamics Simulation In classical molecular dynamics simulations, the classical interatomic potentials are used to crudely approximate the true quantum mechanical potentials since classical forces can be rapidly evaluated. State of the art classical molecular dynamics scheme can calculate the atoms with size up to multimillion atoms. Vashishta et al. constructed meaningful models of glassy GeSe2 and other amorphous materials. Tight-binding Molecular Dynamics Simulation Tight-binding molecular dynamics (TBMD) is designed to run moderate molecular dynamics simulation within the semi-empirical tight-binding scheme. The electronic structure of the simulated system is calculated by a TB hamiltonian so that the quantum mechanical many-body nature of the interatomic forces is naturally taken into account. Sankey and Allen used a tight binding Hamiltonian to do MD first in 1986. The best order N TBMD code now can calculate with size up to several thousand atoms. Ab initio Molecular Dynamics Simulation In mid eighties, Car and Parrinello showed how to combine the accuracy of ab initio density functional methods with force calculations and molecular dynamics techniques. In ab initio MD, the nuclei are treated as classical particles which move in a potential determined by the atomistic force calculated by the density functional theory due to Kohn, Hohenberg and Sham. Now, the state of art MD simulation can be applied for several hundred atoms. For ab initio method, the only information which must be provided are the atomic numbers and positions of the atoms within the system. In contrast, empirical or semi-empirical approaches require a model of the interactions between the atoms to be supplied. The parameters of these models are usually derived by fitting the outcome of simulations to experimental data. Problems with these techniques arise when one considers the range of their applicability. If the parameters of the models were derived from system A, what guarantee is there that they apply to system B with different chemical bonding and/or topology? In a disordered environment, it is very hard to find a universal set of parameters for the classical or semi-classical potentials. As a result, large numbers of fitting parameters are usually needed for either empirical potentials or tight-binding models. In this respect, ab initio MD in which the interatomic potential is determined by the electronic structure of the system is the method of choice to model complex amorphous materials. [ Last edited by fegg7502 on 2009-12-8 at 23:59 ] |
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