High Quality Content by WIKIPEDIA articles! In molecular dynamics, orbit, and particle simulations, energy drift is the gradual change in the total energy of a closed system. According to the laws of mechanics, the energy should be a constant of motion and should not change. However, the energy does fluctuate on a short time scale and increase on a very long time scale due to numerical integration artifacts that arise with the use of a finite time step ?t.Energy drift - usually damping - is substantial for numerical integration schemes that are not symplectic, such as the Runge-Kutta family. Symplectic integrators usually used in molecular dynamics, such as the Verlet integrator family, exhibit increases in energy over very long time scales, though the error remains roughly constant. These integrators do not in fact reproduce the actual Hamiltonian mechanics of the system; instead, they reproduce a closely related "shadow" Hamiltonian whose value they conserve many orders of magnitude more closely. The accuracy of the energy conservation for the true Hamiltonian is dependent on the time step.

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