Theoretical Study On Dynamics Of Condensed-state Systems

Study of the structure and dynamics in condense matter contribute to a broad range of research fields including energy,environmental research,biology as well as material science.People expect to explore the causes and evolution of microscopic physical mechanisms from different spatial and temporal scales,and build a perfect physical picture,thus promote the development of related fields.However,it is often difficult to accurately describe the microscopic structure and dynamic of the research system due to the limited characterization of experimental means,and different detection methods may even provide the opposite conclusion.Therefore,the combination of theoretical simulation with experimental detection is usually applied to merge the limitations and differences in depiction of structure and dynamics from variable experimental measurements,and provide reliable micro-physical picture.Quantitatively compared with experimental detection signal,theoretical simulation not only can analysis the physical picture hidden in the experimental data,but also guide the experiment and predict the experimental results.Otherwise,experiments also help to improve and refine the theoretical model which can provide more accurate physical picture of the microscopic dynamics process.The tightly integrate and spiral development between theory simulation and experiment detection effectively deepen the understanding of dynamics in the condensed phase system,and promote the development of related research fields.Many chemical and most biological processes take place in the ionic aqueous solutions,therefore the study of solution structure and dynamics play an important role in chemical and biophysical research.However,the usual tools for probing solution structures suffer due to the weak contribution of ion-ion correlations to a total scattering pattern.In this dissertation,cooperated with fs IR experiment,we study the atom-level structure and dynamics of ion clustering by applying molecular dynamics simulation.Also in solution environments,protein conformational dynamics is one of the central topics in life science.Infrared spectroscopy is one of the most commonly employed tools for probing the protein folding.However,the experimental protein vibrational spectra are usually complex and congested,its interpretation can benefit tremendously from theoretical modeling and analysis.Combined with MD simulation and spectral modeling,we have proposed a cost-effective approach to simulate the thermal unfolding infrared spectra.The vibrational spectra achieved by this approach well reproduced temperature dependent spectroscopic features in real solution,thus can contribute to understand polypeptide's conformational change and related IR spectra across its thermal unfolding transition.The protocol also showed the ability to discriminate structurally similar polypeptides' folding landscape.In the face of energy shortages,thermoelectric and photovoltaic materials as clean and renewable energy resources have attracted intense attention over the past few decades.Understanding the carrier transport dynamics within thermoelectric materials,contributes to promote the development of new high-performance materials.Cooperated with experiments,we succeed in qualitatively depicting the carrier transport dynamics of heavily doping and multiphase systems and analyzing the inherent causes of dramatically enhanced thermoelectric performance by using Boltzmann transport theory and simplified carrier scattering model.Meanwhile,we briefly introduces the study of carrier transport dynamics in 2D Van der Waals heterostructures optoelectronic devices:electron-hole pair created by light,charge separation,electrons transferring across the heterojunction.and interlayer exciton dynamics.This dissertation consists of six chapters:The first chapter presents the background knowledge and a comprehensive review of relevant literature.It starts with a brief introduction to aqueous solution structure and dynamics.Then it focuses on the ion effect on the water molecules dynamics and ion dynamics in aqueous solution.Moreover,we briefly introduce the research of protein folding mechanism in solution system.And,Amide I vibrational dynamics,Infrared Spectroscopy Theory and Nolinear Exciton Propagtion are briefly introduced.At the end of this chapter,the development of thermoelectric materials,the latest developments in thermoelectric materials,and the brief introduction of Boltzmann transport theory are introduced.In the second chapter,we briefly introduce the theoretical background knowledge of molecular dynamics simulation and first-principles calculation.In the third chapter,combined with fs IR experiment,we carry out the study on aqueous solution structure and dynamics by applying molecular dynamics simulation.The MD simulations based on different force field well reproduce the major features of neutron scattering experimental data.However,unlike the experimental results of neutron scattering,both MD calculations and resonant energy transfers experiments clearly demonstrate that substantial amounts of ion pairs and small ion clusters do exist in the solutions of concentrations,thus clarify the misunderstanding of the neutron scattering experiment.In the fourth chapter,combined with molecular dynamics simulation and theoretical spectral simulation method,we propose a cost-effective approach to simulate the thermal unfolding infrared spectra.The simulated vibrational spectra well reproduced temperature dependent spectroscopic features in real solution,thus can contribute to understand polypeptide's conformational change and related IR spectra across its thermal unfolding transition.In addition,the protocol also shows the ability to discriminate structurally similar polypeptides' folding landscape.Thus,we successfully search for the physical origin of the molecular level that induced the change of the characteristic of the spectral signal,and promote the understanding of the structural change of the protein during the folding process.In the fifth chapter,cooperated with experimental research,we succeed in depicting the carrier transport dynamics of different doping material and analyzing the inherent causes of dramatically enhanced thermoelectric performance.Applying for the simplified carrier scattering model,we reveal the different scattering mechanisms implied by the anisotropy of Seebeck coefficient in Ti doped WS2.Furthermore,the theoretical analysis of multiphase system(oxygen doped MoS2),indicates that the overall nonmonotonic trend of the Seebeck coefficient is contributed to the balance between the reducing effect of the carrier concentration and the enhancing effect of energy filtering.In the last chapter,combined with first principle calculation and simplified Coulomb potential,we numerically simulate the charge transfer excitons across 2D Van der Waals heterostructures surfaces.Meanwhile,we briefly introduce the urgent need for theoretical study of carrier transport dynamics in 2D heterostructures:electron-hole pair creation,separation and exciton dynamics,and prospects for the future.