Wedekind Jan, Reguera David, Strey Reinhard
Institut für Physikalische Chemie, Universität zu Köln, Luxemburger Strasse 116, D-50939 Köln, Germany.
J Chem Phys. 2007 Aug 14;127(6):064501. doi: 10.1063/1.2752154.
We investigate the influence of carrier gas and thermostat on molecular dynamics (MD) simulations of nucleation. The task of keeping the temperature constant in MD simulations is not trivial and an inefficient thermalization may have a strong influence on the results. Different thermostating mechanisms have been proposed and used in the past. In particular, we analyze the efficiency of velocity rescaling, Nose-Hoover, and a carrier gas (mimicking the experimental situation) by extensive MD simulations. Since nucleation is highly sensitive to temperature, one would expect that small variations in temperature might lead to differences in nucleation rates of up to several orders of magnitude. Surprisingly, the results indicate that the choice of the thermostating method in a simulation does not have--at least in the case of Lennard-Jones argon--a very significant influence on the nucleation rate. These findings are interpreted in the context of the classical theory of Feder et al. [Adv. Phys. 15, 111 (1966)] by analyzing the temperature distribution of the nucleating clusters. We find that the distribution of cluster temperatures is non-Gaussian and that subcritically sized clusters are colder while postcritically sized clusters are warmer than the bath temperature. However, the average temperature of all clusters is found to be always higher than the bath temperature.
我们研究了载气和恒温器对成核分子动力学（MD）模拟的影响。在MD模拟中保持温度恒定并非易事，低效的热化过程可能会对结果产生强烈影响。过去已经提出并使用了不同的恒温机制。特别是，我们通过广泛的MD模拟分析了速度重标、诺思-胡佛以及载气（模拟实验情况）的效率。由于成核对温度高度敏感，人们可能会预期温度的微小变化可能导致成核速率相差几个数量级。令人惊讶的是，结果表明模拟中恒温方法的选择——至少在 Lennard-Jones 氩气的情况下——对成核速率没有非常显著的影响。通过分析成核团簇的温度分布，在费德等人的经典理论[《高等物理学》15, 111 (1966)]的背景下对这些发现进行了解释。我们发现团簇温度的分布是非高斯的，并且亚临界尺寸的团簇比浴温更冷，而临界后尺寸的团簇比浴温更热。然而，发现所有团簇的平均温度总是高于浴温。
