Barrett Jonathan C
Nuclear Department, DCEME, HMS Sultan, Military Road, Gosport PO12 3BY, United Kingdom.
J Chem Phys. 2007 Feb 21;126(7):074312. doi: 10.1063/1.2698424.
Decay rates of small clusters (containing between 10 and 40 Lennard-Jones atoms) are determined by molecular dynamics simulations. The cluster is defined by the condition that the atoms must lie within a specified distance of their center of mass, and initial isothermal states are generated using a Metropolis Monte Carlo method. Plots of the logarithm of the survival fraction against time are found to be nonlinear, indicating that the decay of constant temperature clusters is non-Markovian and depends on the collision rate with a thermalizing gas. However, when the clusters are banded according to their energies, exponential decay is seen. The energy dependent decay rates from simulations agree to within a factor of 2 with those estimated from equilibrium considerations (using free energies from thermodynamic integration and assuming a Gaussian energy distribution), indicating that clusters defined in this way can be used in Markovian rate equations. During nucleation, the cluster energy distribution is shifted from its equilibrium value, leading to a reduction in the nucleation rate by a temperature dependent factor of 100 or more, in the absence of a thermalizing carrier gas.
通过分子动力学模拟确定了小团簇（包含10到40个 Lennard-Jones 原子）的衰变率。团簇由原子必须位于其质心指定距离内的条件定义，并且使用 metropolis 蒙特卡罗方法生成初始等温状态。发现存活分数的对数与时间的关系图是非线性的，这表明恒温团簇的衰变是非马尔可夫的，并且取决于与热化气体的碰撞率。然而，当根据团簇的能量进行分组时，可以看到指数衰变。模拟中与能量相关的衰变率与根据平衡考虑估计的衰变率（使用热力学积分的自由能并假设高斯能量分布）在2倍的范围内一致，这表明以这种方式定义的团簇可用于马尔可夫速率方程。在成核过程中，团簇能量分布从其平衡值发生偏移，在没有热化载气的情况下，导致成核率降低100倍或更多的温度相关因子。
