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Optics of Organic Nanomaterials
Published in Vladimir I. Gavrilenko, Optics of Nanomaterials, 2019
A molecular crystal could be defined as a solid that is formed by electrically neutral molecules interacting via weak non-bonding interactions, primarily van der Waals (Silinsh and Capek, 1994). If the constituent molecules possess specific functional groups then the possibility also exists for the formation of hydrogen bonds and dipolar interactions that will also serve to stabilize the crystal. In general, there is little electronic charge overlap between molecules, and therefore the constituent molecules retain their identity to a large extent. This is in contrast to covalent or ionic solids, where the individual properties of constituent particles in the crystal are completely lost. The present chapter overviews optical properties of molecular aggregates, molecular crystals, and molecular-solid systems focusing on specific features related to the nanostructures.
Nonlinear Optical Properties of Semiconductors, Principles, and Applications
Published in Inamuddin, Mohd Imran Ahamed, Rajender Boddula, Tariq Altalhi, Optical Properties and Applications of Semiconductors, 2023
Muhammad Rizwan, Aleena Shoukat, Asma Ayub, Iqra Ilyas, Ambreen Usman, Seerat Fatima
Special requirement for molecular crystals is the crystalline phase, while specific requirements for polymeric materials and monomers are the efficiency of nanostructures. The key features that make the use of organic molecular crystals suitable for the stated applications include a wide area of transparency, strong birefringence, high nonlinear coefficient, high laser light optical thresholds, and flexibility of the molecular structures that can be modified by molecular engineering to optimize the properties of interest. Since the huge exploration of organic materials exists at large in optical nonlinearities, the involvement of these materials has increased, opening up new directions for research and development in the field of photonics (Stanculescu et al. 2011).
Synthetic Nanostructures as Quantum Control Systems
Published in Günter Mahler, Volkhard May, Michael Schreiber, Molecular Electronics, 2020
Molecular crystals are composed of (organic) molecules, which retain, to some extent, their individuality. It is a natural network, often strongly anisotropic. However, the network character is likely to show up only for larger molecules, if at all; the hierarchical complexity is apparently too small otherwise. Most protein macromolecular crystals have lattice constants between 50 and 150 Å.
Factors affecting the cold flow properties of biodiesel: Fatty acid esters
Published in Energy Sources, Part A: Recovery, Utilization, and Environmental Effects, 2018
Chao Yang, Kangkang He, Yuan Xue, Yong Li, Hualin Lin, Han Sheng
According to the crystallization theory, molecular crystals were formed by the interaction between molecules, and for organic molecules, they would be arranged in a close packed arrangement when they were cooled down. In the case of homologs, the greater the molar mass was, the higher the melting point would be; thus, crystallization became easier as well. Actually, the molar mass of a saturated straight chain such as C14:0, C18:0, and C22:0 was increased one by one, and their melting point gradually increased. As a result, a high content of C22:0 in biodiesel would make its cold flow property worse than that of C14:0 and C18:0, as depicted in Figure 1. Regarding the unsaturated carbon chains such as C18:1, C20:1, and C22:1, their molecular structures were no more straight, as shown in Figure 5 (2) and (3); a high content of them in biodiesel would prevent saturated straight chains from being arranged closely owing to space resistance. As such, it would be difficult for wax crystals to form and they tended to be small in size as shown in Figure 6 (1) and (2).
CrySPY: a crystal structure prediction tool accelerated by machine learning
Published in Science and Technology of Advanced Materials: Methods, 2021
Tomoki Yamashita, Shinichi Kanehira, Nobuya Sato, Hiori Kino, Kei Terayama, Hikaru Sawahata, Takumi Sato, Futoshi Utsuno, Koji Tsuda, Takashi Miyake, Tamio Oguchi
We generated 50 random molecular crystal structures using the above settings to validate whether a stable structures can be obtained. Total energy calculations and local structure optimizations were carried out using the density functional theory (DFT) with the projector-augmented wave (PAW) method [36] with the VASP code [29]. The generalized gradient approximation (GGA) by Perdew, Burke, and Ernzerhof [37] was employed for exchange-correlation functional. A cutoff energy of 625 eV for the plane-wave expansion of the wave function and -point mesh density of 80 Å were used. The atomic coordinates and cell parameters were fully optimized until forces acting on every atom became at least smaller than 0.01 eV/Å. Figure 2 shows the most and second most stable structures predicted by our CSP simulation. Space group of the most and second most stable structures are and , respectively. The total energy difference between them is only 10 meV/atom. Unfortunately, the former () was not observed in the experiment, while the latter () was obtained and is known as a stable structure, -LiPS [38]. This can happen because the calculated energy difference is much smaller than the chemical accuracy (1 kcal/mol = 43 meV/atom). We might evaluate the total energy of the former structure a little too low with the DFT calculation. The predicted and experimental crystal parameters of -Li were listed in Table 2. It is an almost perfect match except for the tiny amount of differences in lattice constants and atomic positions. These results demonstrate that the symmetric molecular structure generation method is quite useful for stable structure predictions of molecular crystals.