Electrocaloric effect in ferroelectric materials:From phase field to first-principles based effective Hamiltonian modeling

Electrocaloric effect(ECE)of ferroelectrics has attracted considerable interest due to its potential application in environmentally friendly solid-state refrigeration.The discovery of giant ECE in ferroelectric thin films has greatly renewed the research activities and significantly stimulated experimental and theoretical investigations.In this review,the recent progress on the theoretical modeling of ECE in ferroelectric and antiferroelectric materials are introduced,which mainly focuses on the phase field modeling and first-principles based effective Hamiltonian method.We firstly provide the theoretical foundation and technique details for each method.Then a comprehensive review on the progress in the application of two methods and the strategies to tune the ECE are presented.Finally,we outline the practical procedure on the development of multi-scale computational method without experiemtal parameters for the screening of optimized electrocaloric materials.

大失谐情况下的V-型三能级原子与光场相互作用

本文研究了一个V-型三能级原子与光场的相互作用．在原子与场大失谐情况下，处于基态能级可绝热消除，即此模型可化为非简并Raman耦合模型；进而提出了其改进型有效哈密顿量；最后得到了简并Raman耦合模型的有效哈密顿量，并借助于矩阵求出了任意时刻波函数的解。

非简并Raman耦合模型的改进型有效哈密顿量

本文研究了一个A一型三能级原子与双模量子腔场的相互作用。在原子—场失谐量较大的条件下,把这个模型化为非简并Raman耦合模型提出了非简并Raman耦合模型的改进型有效哈密顿量,给出了其适用条件。分析表明,在研究Raman耦合模型时,通常的有效哈密顿量是不合适的,必须计及原子能级(起码能级之一)的交流Srark移动的影响。

用推转玻尔-莫特森哈密顿量研究A～190区超形变带

用推转玻尔－莫特森哈密顿量研究了Ａ～１９０区２０个核的５５条超形变带．通过拟合实验测得的Ｅ２跃迁能量值，确定了各带的能级自旋，得到了质量参量Ｂ１和硬度参数Ｃ０．

基于哈密顿随机效应的运维系统动态数据迁移模型

借鉴运维系统动态数据迁移理念,提出了一种基于哈密顿随机效应的运维系统动态数据迁移模型(Dynamic data migration model of operation and maintenance system,DDMMOMS).根据运维系统动态数据迁移的核心理论,针对常用的动态数据迁移,设计了运维系统动态数据迁移模型.利用该模型能够将快速哈密顿随机效应应用于目标区域中,其智能性十分突出.最后通过仿真实验表明:该运维系统动态数据迁移模型方法稳定性高、鲁棒性强,在速度以及寻优能力等都具有较好表现.

A review on different theoretical models of electrocaloric effect for refrigeration

The performance parameters for characterizing the electrocaloric effect are isothermal entropy change and the adiabatic temperature change,respectively.This paper reviews the electrocaloric effect of ferroelectric materials based on different theoretical models.First,it provides four different calculation scales(the first-principle-based effective Hamiltonian,the Landau-Devonshire thermodynamic theory,phase-field simulation,and finite element analysis)to explain the basic theory of calculating the electrocaloric effect.Then,it comprehensively reviews the recent progress of these methods in regulating the electrocaloric effect and the generation mechanism of the electrocaloric effect.Finally,it summarizes and anticipates the exploration of more novel electrocaloric materials based on the framework constructed by the different computational methods.

Yb^3+掺杂稀土钽铌酸盐的晶体场从头计算研究

Yb^3+掺杂晶体材料是重要的激光材料,在超短脉冲激光、大功率激光等领域有重要应用前景,但长期以来很难通过实验拟合确定Yb^3+晶体场参数,尤其是低对称体系,从头计算是解决此问题的重要途经。本文介绍了适合计算稀土离子掺杂晶体的从头计算DV-Xα方法和有效哈密顿量模型,用该方法计算了Yb^3+掺杂M型和M’型钽铌酸盐的晶场参数和旋轨耦合参数,得到的能级结构和实验能很好地符合,并发现了Yb^3+掺杂钽铌酸盐的晶场强度参数随稀土原子序数呈现规律变化。表明结合DV-Xα计算和有效哈密顿量方法是计算Yb^3+掺杂低对称钽铌酸盐晶体场的有效途径,结果显示Yb^3+掺杂钽铌酸盐晶体有望成为新型全固态激光工作物质。

从头计算法计算Yb^(3+)掺杂钽酸盐的晶体场参数和能级结构

介绍了一种基于从头计算的DV-Xα方法和有效哈密顿量模型,它可以计算晶体中掺杂离子的晶体场参数和旋轨耦合参数,尤其适合计算低对称性的晶体.对于低对称性的晶体,参数的数目比能级的数目多,因此通过实验能级拟合确定所有的参数不太准确,而从头计算法可以准确地确定所有的晶体场参数和旋轨耦合参数.首先用这种模型计算了Yb3+掺杂GdTaO4晶体中的晶体场参数和旋轨耦合参数,然后给出了Yb3+在GdTaO4中的能级结构,并分析了Yb3+:GdTaO4的发射谱形成一个连续的发射带.这有利于激光的调谐和锁模激光输出,预言了Yb3+:GdTaO4有望成为新型全固态超短脉冲激光工作物质.同样用这种模型分别计算了Yb3+掺杂YTaO4和ScTaO4中的晶体场参数和旋轨耦合参数,并给出了Yb3+在YTaO4和ScTaO4中的能级结构,得到了与Yb3+:GdTaO4晶体类似的结论.

Theory and algorithms for the excited states of large molecules and molecular aggregates

This project aims to attack the frontiers of electronic structure calculations on the excited states of large molecules and molecular aggregates by developing novel theoretical and computational methods. The methodology development is especially based on the time-dependent density functional theory (TDDFT) and valence bond (VB) theory, and is expected to be computationally effective and accurate as well. Research works on the following related subjects will be performed: (1) The analytical energy-derivative approaches for electronically excited state within TDDFT will be developed to reduce bypass the computational costs in the calculation of molecular excited-state properties. (2) The ab initio methods for electronically excited state based on VB theory and hybrid TDDFT-VB method will be developed to overcome the limitations of current TDDFT in simulating photophysics and photochemistry. (3) For larger aggregates, neither ab initio methods nor TDDFT is applicable. We intend to build the effective model Hamiltonian by developing novel theoretical and computational methods to calculate the involved microscopic physical parameters from the first-principles methods. The constructed effective Hamiltonian is then used to describe the excitonic states and excitonic dynamics of the natural or artificial photosynthesized systems, organic or inorganic photovoltaic cell. (4) The condensed phase environment is taken into account by combining the developed theories and algorithms based on TDDFT and VB with the polarizable continuum solvent models (PCM), molecular mechanism (MM), classical electrodynamics (ED) or molecular dynamics (MD) theory. (5) Highly efficient software packages will be designed and developed.

Theoretical methods for excited state dynamics of molecules and molecular aggregates

This contribution provides a summary of proposed theoretical and computational studies on excited state dynamics in molecular aggregates, as an important part of the National Natural Science Foundation (NNSF) Major Project entitled "Theoretical study of the low-lying electronic excited state for molecular aggregates". This study will focus on developments of novel methods to simulate excited state dynamics of molecular aggregates, with the aim of understanding several important chemical physics processes, and providing a solid foundation for predicting the opto-electronic properties of organic functional materials and devices. The contents of this study include: (1) The quantum chemical methods for electronic excited state and electronic couplings targeted for dynamics in molecular aggregates; (2) Methods to construct effective Hamiltonian models, and to solve their dynamics using system-bath approaches; (3) Non-adiabatic mixed quantum-classic methods targeted for molecular aggregates; (4) Theoretical studies of charge and energy transfer, and related spectroscopic phenomena in molecular aggregates.