In the presence of a (time-dependent) macroscopic electric field the electron dynamics of dielectrics cannot be described by the time-dependent density only. We present a real-time formalism that has the density and the macroscopic polarization P as key quantities. We show that a simple local function of P already captures long-range correlation in linear and nonlinear optical response functions. Specifically, after detailing the numerical implementation, we examine the optical absorption, the second- and third-harmonic generation of bulk Si, GaAs, AlAs and CdTe at different level of approximation. We highlight links with ultranonlocal exchange-correlation functional approximations proposed within linear response time-dependent density functional theory framework.
An accurate estimate of the ferroelectric polarization in ferroelectric-dielectric stacks is important from a materials science perspective, and it is also crucial for the development of ferroelectric based electron devices. This paper revisits the theory and application of the PUND technique in Metal-Ferroelectric-Dielectric-Metal (MFDM) structures by using analytical derivations and numerical simulations. In an MFDM structure the results of the PUND technique may largely differ from the polarization actually switched in the stack, which in turn is different from the remnant polarization of t…
Origin of Large Dielectric Constant with Large Remnant Polarization and Evidence of Magnetoelectric Coupling in Multiferroic La modified BiFeO3-PbTiO3 Solid Solution
The induced surface charges appear to diverge when dielectric particles form close contacts. Resolving this singularity numerically is prohibitively expensive because high spatial resolution is needed. We show that the strength of this singularity is logarithmic in both inter-particle separation and dielectric permittivity. A regularization scheme is proposed to isolate this singularity, and to calculate the exact cohesive energy for clusters of contacting dielectric particles. The results indicate that polarization energy stabilizes clusters of open configurations when permittivity is high, i…
Weakly coupled ferroelectric/dielectric superlattice thin film heterostructures exhibit complex nanoscale polarization configurations that arise from a balance of competing electrostatic, elastic, and domain-wall contributions to the free energy. A key feature of these configurations is that the polarization can locally have a significant component that is not along the thin-film surface normal direction, while maintaining zero net in-plane polarization. PbTiO3/SrTiO3 thin-film superlattice heterostructures on a conducting SrRuO3 bottom electrode on SrTiO3 have a room-temperature stripe nanodo…
ZStar: A unified toolkit for polarization, Born effective charges, dielectric and piezoelectric responses, and infrared and Raman spectra
Institute of Artificial Intelligence, Hefei Comprehensive National Science Center（合肥综合性国家科学中心人工智能研究院）；CAS Key Laboratory of Quantum Information, University of Science and Technology of China（中国科学技术大学量子信息重点实验室）；Hefei National Laboratory, University of Science and Technology of China（中国科学技术大学合肥国家实验室）
Static dielectric response and Born effective charge of BN nanotubes from {\it ab initio} finite electric field calculations
用有限电场方法对BN纳米管（BN-NTs）的全静态介电响应和Born有效电荷进行了{\it Ab initio}研究。据发现，离子的贡献的BN-NTs的静态介电响应是实质性的，也是一个明显的手性依赖的振荡叠加在纵向电极化率和管直径（$D$）之间的线性关系，作为一个薄的介电圆柱壳。相比之下，BN-NT的横向介电响应类似于直径为$D+4$·$ $的薄（非理想）导电圆柱壳的行为，其中内部电场的屏蔽因子为2。玻恩有效电荷的中等主分量$Z_y^*$对应于与BN-NT表面相切的横向原子位移，具有明显的$D$依赖性（但与手性无关），而大的纵向分量$Z_z^*$表现出明显的手性依赖性（但几乎与$D$无关），这表明了表征BN-NT的直径和手性的强有力的方法。
Electro-optic switching of dielectrically negative nematic through nanosecond electric modification of order parameter (NEMOP)
我们目前的实验研究纳秒电修改的序参量（NEMOP）在各种负介电各向异性的介电材料。该研究表明，NEMOP能够实现大幅度的快速（纳秒）电光响应，场致双折射的数量级为0.01，品质因数（FoM）的数量级为$10^4$ $μ$ m $^2/$ s;后者的数量级高于传统上用于电光MEMS器件的弗雷德里克效应的FoM。NEMOP响应的幅度通常在具有较大介电各向异性和较高自然（无场）双折射的向列相中更强。
Energy Research Institute（能源研究院）；Nanyang Technological University（南洋理工大学）
Solving physics problems for which we know the equations, boundary conditions and symmetries can be done by deep learning. The constraints can be either imposed as terms in a loss function or used to formulate a neural ansatz. In the present case study, we calculate the induced field inside and outside a dielectric cube placed in a uniform electric field, wherein the dielectric mismatch at edges and corners of the cube makes accurate calculations numerically challenging. The electric potential is expressed as an ansatz incorporating neural networks with known leading order behaviors and symmet…
