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Numerical distortion and effects of thermostat in molecular dynamics simulations of single-walled carbon nanotubes
李 瑞, 胡元中, 王 慧, 张宇军
2008 (11):
4253-4259.
doi: 10.1088/1674-1056/17/11/049
摘要
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In this paper, single-walled carbon nanotubes (SWCNTs) are studied
through molecular dynamics (MD) simulation. The simulations are
performed at temperatures of 1 and 300\,K separately, with atomic
interactions characterized by the second Reactive Empirical Bond
Order (REBO) potential, and temperature controlled by a certain
thermostat, i.e. by separately using the velocity scaling, the
Berendsen scheme, the Nose--Hoover scheme, and the generalized
Langevin scheme. Results for a (5,5) SWCNT with a length of 24.5\,nm
show apparent distortions in nanotube configuration, which can
further enter into periodic vibrations, except in simulations using
the generalized Langevin thermostat, which is ascribed to periodic
boundary conditions used in simulation. The periodic boundary
conditions may implicitly be applied in the form of an inconsistent
constraint along the axis of the nanotube. The combination of the
inconsistent constraint with the cumulative errors in calculation
causes the distortions of nanotubes. When the generalized Langevin
thermostat is applied, inconsistently distributed errors are
dispersed by the random forces, and so the distortions and
vibrations disappear. This speculation is confirmed by simulation in
the case without periodic boundary conditions, where no apparent
distortion and vibration occur. It is also revealed that numerically
induced distortions and vibrations occur only in simulation of
nanotubes with a small diameter and a large length-to-diameter
ratio. When MD simulation is applied to a system with a particular
geometry, attention should be paid to avoiding the numerical
distortion and the result infidelity.
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