Chai Ziwei, Luber Sandra
Department of Chemistry, University of Zurich, Winterthurerstrasse 190, 8057 Zurich, Switzerland.
J Chem Theory Comput. 2024 Sep 6. doi: 10.1021/acs.jctc.4c00671.
In electrochemical experiments, the number of electrons of the electrode immersed in the electrolyte is usually variable. Additionally, the numbers of adsorbed substances on the surface of the electrode, the solvent molecules, and counter charge ions in the near-surface region can also vary. Treating electrochemical solid-liquid interfaces with the typical fixed electron number density functional theory (DFT) approach tends to be a challenge. This can be addressed by using grand canonical ensemble approaches. We present the implementation of two grand canonical ensemble approaches in the open-source computational chemistry software CP2K that go beyond the existing canonical ensemble paradigm. The first approach is based on implicit solvent models and explicit atomistic solute (electrode with/without adsorbed species) models, and includes two recent developments: (a) grand canonical self-consistent field (GC-SCF) method ( 114104) allowing the electron number of the system to fluctuate naturally and accordingly with the experimental electrode potential, (b) planar counter charge ( 041722, 245416) salt model completely screening the net charge of the electrode model. In contrast with previous studies, in our implementation, the work function (WF) (absolute electrode potential if the potential drop at the electrolyte-vacuum interface is omitted) is the constrained quantity during an SCF optimization instead of the Fermi energy. The chemical potential of electrons (negative WF) is a natural variable of the grand potential in the GC ensemble of electronic states, and this method can easily achieve stable SCF convergence and obtain an electronic structure that precisely corresponds to a user-specified WF. The second approach referred to as the GC DFT molecular dynamics (DFT-MD) simulation scheme ( 213002, 234505, (12) 3928-3938) is based on fully explicit modeling the solvent molecules and the ions and is used to calculate the electron chemical potential corresponding to an equilibrium electrochemical half-reaction ( + ⇌ ) which involves DFT-MD, by allowing the number of electrons to vary during the DFT-MD simulation process. This opens the way for forefront electrochemical calculations in CP2K for a broad range of systems.
在电化学实验中，浸入电解质中的电极的电子数通常是可变的。此外，电极表面吸附物质、溶剂分子以及近表面区域中反电荷离子的数量也会变化。用典型的固定电子数密度泛函理论（DFT）方法处理电化学固液界面往往具有挑战性。这可以通过使用巨正则系综方法来解决。我们展示了在开源计算化学软件CP2K中实现的两种巨正则系综方法，它们超越了现有的正则系综范式。第一种方法基于隐式溶剂模型和显式原子溶质（有/无吸附物种的电极）模型，并且包括两个最新进展：（a）巨正则自洽场（GC-SCF）方法（114104），允许系统的电子数自然波动，并与实验电极电位相应波动，（b）平面反电荷（041722，245416）盐模型，完全屏蔽电极模型的净电荷。与之前的研究不同，在我们的实现中，功函数（WF）（如果忽略电解质-真空界面处的电位降，则为绝对电极电位）是自洽场优化过程中的约束量，而不是费米能量。电子的化学势（负WF）是电子态巨正则系综中巨势的自然变量，并且这种方法可以轻松实现稳定的自洽场收敛，并获得与用户指定的WF精确对应的电子结构。第二种方法称为GC DFT分子动力学（DFT-MD）模拟方案（213002，234505，(12) 3928 - 3938），基于对溶剂分子和离子的完全显式建模，并用于计算对应于平衡电化学半反应（+⇌）的电子化学势，这涉及通过在DFT-MD模拟过程中允许电子数变化的DFT-MD。这为CP2K中针对广泛系统的前沿电化学计算开辟了道路。
