Studies On The Dynamic Properties Of Excess Electron In Homogeneous System By Ab Initio Molecular Dynamics Simulations

Charge transfer and proton transfer are one of the fundamental questions in chemistry and life science. Widespread special interests have been attracted on solvation of excess electrons largely due to its high mobility and activity. As excess electrons are the most fundamental chemical reagents as well as carriers of negative charge, substantial experimental and theoretical efforts have focused on elucidating their equilibrium structure and solvation dynamics in a variety of system. A common recognize is that once an excess electron is injected to a liquid system, it is trapped inside solvent cavity, and the electron movement may be described by a s-like function for ground electronic state and a p-like function for the possible excited state. Dynamic property of excess electron is of fundamental importance to the unraveling of key chemical and biological processes and also are the main difficulties of life and material science encountered today. Thus, in the present dissertation, Ab initio molecular dynamics simulations have been performed to investigate the equilibrium structure and solvation dynamics of excess electron in different media and different electron state. On the basis of the prevenient studies, some simulations have been performed to characterize the role of excess electron in material and life science. Then the aim to reveal the secret of charge transfer can be carried out step by step. We carried out a series of significative work and obtained some valuable results on these issues. The primary innovations are related as follows.(1) Evolution of hydrated electron in water solution. Ab initio molecular dynamics simulations indicate that, different from e-aq mentioned usually, the singlet e22-aq can survive in a cavity composed of 5-6 H2O molecules reoriented by pointing their dangling hydrogens toward the trapped singlet dielectron at about hundred femto-second time scale, slightly longer than the lifetime of e-aq. More interesting is that the singlet e22-aq cavity can not transform from one to another only by reorganizing the cavity water shell in a manner in e-aq, instead, it starts to distort with the cooperative shape-change of the localized cloud after a ～120 fs period for survival, and a proton of a H2O in the primary shell quickly transfers to the center zone of the singlet e22-aq cavity, exhibiting a novel proton transfer process. As a result, a hydrated hydride anion (H-aq) is generated with the lifetime of ca.20 fs. Immediately, the second proton starts to migrate toward H- from another primary shell H2O, and then a molecular hydrogen (H2) formed. In a concerted manner, the yielded residue hydroxide anions (OH-) and the other solvent waters further reorganize to reach a new equilibrium, forming two distinctly separated OH-aq structures. This work presents the first detailed analysis regarding the evolution dynamics of e22-aq for the understanding of the radiolysis-induced reactions in solution.(2) Solvation of excess electrons in LiF ionic pair matrix. Ab initio molecular dynamics simulations and first-principles calculations reveal the existence of solvated dielectron, (2e)s-,in LiF ionic matrix. The nature of the solvation mechanism and the stable existence was explored. Once an excess electron is injected to the LiF ionic matrix, single electron solvation cavity could be generated during the simulation, and the formed cavities mainly exhibit as from 2mer to 4mer. Injection of two singlet excess electrons could cause formation of solvated dielectron, and the observed cavities behave mainly as 4mer to 6mer. Two triplet excess electron could form two solvated electron during the simulation, and two electrons occupy two separated cavity cores in spin-parallel, respectively. Namely, solvated dielectron at triplet state behaves as two solvated single electrons. In addition to the electrostatic interaction, the hole-orbital coupling among solvent molecules may significantly enhance the stability of the solvated electrons, and governs the extent of electron solvation. This hole-orbital coupling is different from either the electrostatic one or the conventional chemical bonding, and may be described as a transition between them.(3) Evolution of positive excess charge Solvation in liquid formaldehyde. Hole transfer (positive charge transfer) is one of the most important part of charge transfer process. Ab initio molecular dynamics simulations of positive excess charge in liquid formaldehyde reveal the dynamic and evolution process of electron hole for the first time. The specific structural properties and solvation process of electron hole have been explored in detail. Simulation reveals that, with the injection of positive charge, the mobility of liquid formaldehyde has been promoted. The activity of oxygen in formaldehyde molecules have been promoted substantially with the influence of positive charge to the lone pair. Meanwhile, the activity of carbon and hydrogen atoms barely changed. Along with the diffusing in the conductive band, the positive excess charge could be localized between O...O form O.'.O three-electron bonds or it could be localized between C...O form O.'.πthree-electron bonds. After injection of positive charge, the electron hole in the liquid formaldehyde system evolves from one state to another, and the localized state of electron hole could survive for 100fs-150fs during the simulation. Moreover, the existence state of electron hole could relate to the HOMO & LUMO gap. HOMO & LUMO gap could decrease if the localized state is formed, and the gap would rise if the electron hole is diffused in the conductive band. This work presents the first detailed analysis regarding the evolution dynamics of positive excess charge for the understanding of the electron hole transfer process in solution.(4) Evolution of excess electron interaction with a solvated protonated arginine residue. The research on the electron behaviors correlated with protonated arginine residue is very important due to its fundamental existence in biological system. Ab initio molecular dynamics simulations of excess electron injected to the protonated arginine residue related system reveal the dynamic properties and evolution process of excess electron interact with the protonated arginine for the first time. The injected excess electron could localize at the protonated arginine from the diffusion state rapidly, forming a stable localized electron structure. And the formed localized electron could survive for 300fs during the simulation. Then the localized electron transfer to the primary shell of solution via nearby water molecule, finally leading to formation of solvated electron in the system. Meanwhile, the negative localized electron at the protonated arginine could keep the nearby hydrogen from primary shell water molecules from departure. The phenomena observed here is largely due to the relatively higher ability of protonated arginine residue to stabilize the excess electron. This work presents the first detailed analysis regarding the evolution dynamics of protonated arginine residue relate excess electron for the understanding of the charge transfer process in biological system.