Modeling of liquid water and ionic solutions by first-principles simulations

Abstract

Water is one of the most important materials and has enormous impacts on life. Due to its delicate Hydrogen bond (H-bond) network, water shows various anomalous properties which has not been fully illuminated. Advanced experimental methods, such as scattering experiments and various spectroscopy techniques, have been developed and applied to study the nature of H-bond in liquid water. On the other hand, ab initio molecular dynamics (AIMD) have been widely adopted as an important theoretical tool to provide microscopic information of water on a sub-picosecond timescale. Recent AIMD studies based on the strongly constrained and appropriately normed (SCAN) exchange correlation functional yield an excellent description of the structural, electronic, and dynamic properties of liquid water. In this dissertation, we will focus on studying the structural, electronic and dynamic properties of liquid water as well as the modeling of the hydration structures of ions in aqueous solutions, using AIMD with potential energy surface provided by the novel SCAN functional. In the first work we represent an accurately predicted infrared spectrum of liquid water and show how the improvements are connected to the description of the underlying H-bond network. The second work mainly focusing on modeling the nuclear quantum effects (NQEs) and isotope effect of liquid water with a force field model based on artificial neural network, where qualitative agreements with experimental observations are achieved. In the third work, we study the isotope effect on the x-ray absorption spectra of liquid and attribute observed differences to the structural distinctions between light and heavy water as mentioned in the previous work. And in the last two projects, we systematically show the necessity of including NQEs of the hydrogen atom when modeling chloride ionic solution. Prominent changes in the hydration structure as well as electronic structure can be identified when NQEs are taken into consideration.