Baptista L A, Dutta R C, Sevilla M, Heidari M, Potestio R, Kremer K, Cortes-Huerto R
Max Planck Institute for Polymer Research, Ackermannweg 10, 55128, Mainz, Germany.
Physics Department, University of Trento, via Sommarive, 14 I-38123 Trento, Italy.
J Phys Condens Matter. 2021 Apr 23;33(18). doi: 10.1088/1361-648X/abed1d.
In the Hamiltonian adaptive resolution simulation method (H-AdResS) it is possible to simulate coexisting atomistic (AT) and ideal gas representations of a physical system that belong to different subdomains within the simulation box. The Hamiltonian includes a field that bridges both models by smoothly switching on (off) the intermolecular potential as particles enter (leave) the AT region. In practice, external one-body forces are calculated and applied to enforce a reference density throughout the simulation box, and the resulting external potential adds up to the Hamiltonian. This procedure suggests an apparent dependence of the final Hamiltonian on the system's thermodynamic state that challenges the method's statistical mechanics consistency. In this paper, we explicitly include an external potential that depends on the switching function. Hence, we build a grand canonical potential for this inhomogeneous system to find the equivalence between H-AdResS and density functional theory (DFT). We thus verify that the external potential inducing a constant density profile is equal to the system's excess chemical potential. Given DFT's one-to-one correspondence between external potential and equilibrium density, we find that a Hamiltonian description of the system is compatible with the numerical implementation based on enforcing the reference density across the simulation box. In the second part of the manuscript, we focus on assessing our approach's convergence and computing efficiency concerning various model parameters, including sample size and solute concentrations. To this aim, we compute the excess chemical potential of water, aqueous urea solutions and Lennard-Jones (LJ) mixtures. The results' convergence and accuracy are convincing in all cases, thus emphasising the method's robustness and capabilities.
在哈密顿自适应分辨率模拟方法（H-AdResS）中，可以模拟属于模拟盒内不同子域的物理系统的共存原子istic（AT）和理想气体表示。哈密顿量包括一个场，当粒子进入（离开）AT区域时，通过平滑地开启（关闭）分子间势来桥接这两个模型。在实际操作中，计算并应用外部单体力以在整个模拟盒中强制达到参考密度，并且由此产生的外部势加到哈密顿量上。这个过程表明最终的哈密顿量明显依赖于系统的热力学状态，这对该方法的统计力学一致性提出了挑战。在本文中，我们明确包含一个依赖于切换函数的外部势。因此，我们为这个非均匀系统构建一个巨正则势，以找到H-AdResS与密度泛函理论（DFT）之间的等价性。我们从而验证诱导恒定密度分布的外部势等于系统的过量化学势。鉴于DFT中外部势与平衡密度之间的一一对应关系，我们发现系统的哈密顿描述与基于在模拟盒中强制达到参考密度的数值实现是兼容的。在论文的第二部分，我们专注于评估我们的方法在各种模型参数（包括样本大小和溶质浓度）方面的收敛性和计算效率。为此，我们计算水、尿素水溶液和 Lennard-Jones（LJ）混合物的过量化学势。在所有情况下，结果的收敛性和准确性都令人信服，从而强调了该方法的稳健性和能力。
