Water adsorption isotherm describes soils’ ability in retaining water under given relative humidity and isothermal conditions, and is frequently utilized to characterize soils’ engineering properties. Fundamentally, the water adsorption isotherm on soil external particle surface is the macroscopic manifestation of atomistic scale soil–water interaction mechanisms, including van der Waals, surface hydration, cation hydration, and electrical double layer. Yet, the quantitative link between these mechanisms and water adsorption isotherms remains obscure, and it still lacks effective approaches to probe these mechanisms. Here, a general framework based on Grand Canonical Monte Carlo simulation was developed to directly obtain water adsorption isotherms on soil external particle surface from the interatomic potentials. The simulated adsorption isotherm agrees well with existing experimental and numerical results, confirming the validity of the proposed framework. The proposed framework facilitates a quantitative assessment of the impact of atomistic scale soil–water interaction mechanisms on the macroscale water adsorption isotherms. It reveals that the atomistic scale soil–water interaction mechanisms dictate the shape of adsorption isotherms, i.e., an ‘S’ shape by prevailing cation hydration and a concave shape by prevailing surface hydroxyl hydration; and divalent cations exhibit a much more intensive interaction with water molecules than univalent cations, increasing the adsorption capacity up to 9.5 times.

吸水等温线描述了土壤在给定的相对湿度和等温条件下保持水分的能力，并且经常被用来表征土壤的工程特性。从根本上说，土壤外部颗粒表面的吸水等温线是原子尺度水土相互作用机制的宏观表现，包括范德华力、表面水化、阳离子水化和双电层。然而，这些机制与水吸附等温线之间的定量联系仍然模糊不清，并且仍然缺乏探索这些机制的有效方法。在这里，开发了基于 Grand Canonical Monte Carlo 模拟的一般框架，以从原子间势直接获得土壤外部颗粒表面的水分吸附等温线。模拟的吸附等温线与现有的实验和数值结果非常吻合，证实了所提出框架的有效性。所提出的框架有助于定量评估原子尺度水土相互作用机制对宏观水吸附等温线的影响。它揭示了原子尺度的土壤-水相互作用机制决定了吸附等温线的形状，即主要的阳离子水合为“S”形，而主要的表面羟基水合为凹形；二价阳离子与水分子的相互作用比单价阳离子强得多，吸附容量增加了 9.5 倍。所提出的框架有助于定量评估原子尺度水土相互作用机制对宏观水吸附等温线的影响。它揭示了原子尺度的土壤-水相互作用机制决定了吸附等温线的形状，即主要的阳离子水合为“S”形，而主要的表面羟基水合为凹形；二价阳离子与水分子的相互作用比单价阳离子强得多，吸附容量增加了 9.5 倍。所提出的框架有助于定量评估原子尺度水土相互作用机制对宏观水吸附等温线的影响。它揭示了原子尺度的土壤-水相互作用机制决定了吸附等温线的形状，即主要的阳离子水合为“S”形，而主要的表面羟基水合为凹形；二价阳离子与水分子的相互作用比单价阳离子强得多，吸附容量增加了 9.5 倍。由主要的阳离子水合导致的“S”形和主要的表面羟基水合导致的凹形；二价阳离子与水分子的相互作用比单价阳离子强得多，吸附容量增加了 9.5 倍。由主要的阳离子水合导致的“S”形和主要的表面羟基水合导致的凹形；二价阳离子与水分子的相互作用比单价阳离子强得多，吸附容量增加了 9.5 倍。