Search

Using the CRYSTAL17 package at the coupled-perturbed Kohn–Sham (CPKS) level, periodic boundary conditions first-principles calculations are enacted to predict the second harmonic generation second-order nonlinear optical (NLO) susceptibility, χ(2), values of six historical NLO crystals. This selection allowed the comparison between state-of-the-art calculations and experiment. Several computational aspects are tackled to define conditions where the results are converged with respect to the range of lattice summations, to the number of k-points in the first Brillouin zone, to the order of the multipole expansions for evaluating the long-range part of the electrostatic interactions, as well as to the atomic basis set size. A valence triple zeta basis set supplemented with polarization functions has been selected. Then, χ(2) calculations have been performed using a range of exchange-correlation functionals (XCFs). Results show the large impact of the amount of Hartree–Fock (HF) exchange on the amplitude but also on the sign on the χ(2) tensor components. To a given extent, these amplitude effects are consistent with results on molecules, but the sign reversal effects and the non-monotonic behavior of the χ(2) tensor components as a function of the amount of HF exchange are scarcely found for molecules. Then, using the recommended range-separated hybrid XCFs, the CPKS scheme leads to good agreement with experimental data for potassium dihydrogenophosphate, urea, and χ ZXX (2) of LiNbO3. The agreement is more questionable for χ ZZZ (2) of LiNbO3 whereas it remains poor for ammonium dihydrogenophosphate and 2-methyl-4-nitroaniline, with large underestimations by about a factor of 3, opening a path to further fine-tuning of the ranges of inclusion of HF exchange. [ABSTRACT FROM AUTHOR]

The quantum treatment of electrons at the Kohn‐Sham Density Functional Theory (DFT) level of approximation is used in order to optimize the structure of four organic and organo‐metallic crystalline systems, starting from experimentally determined structures, allowing subsequent quantum‐level theoretical analysis, the accent here being put on crystals having nonlinear optical (NLO) properties. By employing DFT, one must select an exchange‐correlation functional (XCF), that is, a mathematical description of the electron interactions. Among most of the XCFs, a well‐known general discrepancy is the lack of London‐type interactions description. One of the most popular correction schemes consists of adding a posteriori the contribution of these interactions by using empirical expressions. Here, the approach relies on the simple D* scheme, a variation of the D2 correction originally elaborated by Grimme for molecular clusters, where the D2 correction is scaled to account for the interactions in the crystal solid state. The performance of this simple D* scheme is demonstrated and the most suitable scaling factors for four prototypical organic and organo‐metallic NLO crystals are determined for four representative XCFs: zero (no correction) for PBESol, PBESol0, and ωB97X, and 0.7 for B3LYP. [ABSTRACT FROM AUTHOR]

In this article, an improved impervious solid boundary condition of the coupled method called smooth particle hydrodynamics and discrete element method (SPH‐DEM) is proposed, which prevents the fluid particles from penetrating solid boundary under earthquake action. And an improved transmitting boundary condition of SPH‐DEM is designed in order to conquer the reflection of seismic waves on the boundary. Meanwhile, the effective stress method is proposed to be applied to the SPH‐DEM for simulating seabed liquefaction. Based on these, a new computational framework for the SPH‐DEM is put forward. Dynamic triaxial test of seabed soil samples indicate that our proposed computational framework can well reproduce the seismic liquefaction process of the seabed soil. Moreover, our proposed computational framework is used to numerically reproduce the failure mechanisms of a breakwater built in liquefied seabed under combined tsunami–earthquake activity and meantime the centrifuge test is carried out. And the experimental results demonstrate the effectiveness of our proposed computational framework, in which numerical results of it are consistent with results of the centrifuge test. [ABSTRACT FROM AUTHOR]

Nonlinear optics is essential for many recent photonic technologies. Here, a novel multi-scale approach is introduced to simulate the nonlinear optical response of molecular nanomaterials combining ab initio quantum-chemical and classical Maxwell-scattering computations. In this approach, the first hyperpolarizability tensor is computed with time-dependent density-functional theory and incorporated into a multi-scattering formalism that considers the optical interaction between neighboring molecules. Such incorporation is achieved by a novel object: the Hyper-Transition(T)-matrix. With this object at hand, the nonlinear optical response from single molecules and also from entire photonic devices can be computed, including the full tensorial and dispersive nature of the optical response of the molecules, as well as the optical interaction between different molecules as, for example, in the lattice of a molecular crystal. To demonstrate the applicability of the novel approach, the generation of a second-harmonic signal from a thin film of an Urea molecular crystal is computed and compared to more traditional simulations. Furthermore, an optical cavity is designed, which enhances the second-harmonic response of the molecular film up to more than two orders of magnitude. This approach is highly versatile and accurate and can be the working horse for the future exploration of nonlinear photonic molecular materials in structured photonic environments., (© 2023 The Authors. Advanced Materials published by Wiley-VCH GmbH.)