Rashid, Md Al Mamunur Rahman, Mofizur Acter, Thamina Uddin, Nizam 2024-01-19T08:03:11Z 2024-01-19T08:03:11Z 2023-11-30 2023-12 1463-9076 https://pubs.kist.re.kr/handle/201004/113045 Controversies on the water surface were theoretically addressed with the help of large scale quantum mechanical molecular dynamics (QMMD) simulations on water surface model systems with and without excess hydroniums and hydroxides. It was revealed that the thermodynamic surface structures of these ions strongly depend on their location and dipole orientation. Fast hydronium diffusion by proton transfer establishes a wider kinetic depth distribution (similar to 6 angstrom) than that predicted by its thermodynamic affinity for the water surface, while slow hydroxide is shallowly trapped below the outermost molecular layer (3-4 angstrom). In addition, the anisotropic orientation of surface water dipole can generate a substantial magnitude of surface potential, which extends to a depth of a few molecular layers. With these distinctively different surface properties of two ions and water molecules, the seemingly contradictory observations of acidic and negatively charged water surfaces may be successfully explained. That is, the negative surface charge of neutral water mostly stems from intrinsic water properties such as water dipole orientation and electron density spillage at the surface, rather than surface OH- ions. The enhanced acidity of the water surface can be attributed in large part to the kinetic depth profile of ion density in addition to static thermodynamic origin. Furthermore, the different depth profiles of the two ions may differently affect the surface-sensitive spectroscopic observations. QM/MD simulations on water surface model systems were performed. The hydronium ion shows strong preference on water surface. The hydroxide ion does not display surface-liking behavior. Anisotropic dipole orientation at the water surface generates negative surface charges. English Royal Society of Chemistry Identifying the acidic or basic behavior of surface water: a QM/MM-MD study Article 10.1039/d3cp02080k 1 Physical Chemistry Chemical Physics, v.25, no.45, pp.31194 - 31205 Physical Chemistry Chemical Physics 25 45 31194 31205 N scie scopus 001100689000001 2-s2.0-85176802110 Chemistry, Physical Physics, Atomic, Molecular & Chemical Chemistry Physics Article LIQUID-VAPOR INTERFACE DYNAMICS QM/EFP-MD MOLECULAR-DYNAMICS AQUEOUS-SOLUTION PROTON-TRANSFER HYDROXIDE IONS HYDRONIUM ASSOCIATIONS MECHANISMS METHANOL