RESUMEN
The weak coupling of a toroidal dipole (TD) to an electromagnetic field offers great potential for the advanced design of photonic devices. However, simultaneous excitation of electric toroidal dipoles (ETDs) and magnetic toroidal dipoles (MTDs) is currently difficult to achieve. In this work, we propose a hybrid metasurface based on Si and phase transition material G e 2 S b 2 S e 4 T e 1 (GSST), which is formed by four Si columns surrounding a GSST column and can simultaneously excite two different TD (ETD and MTD) resonances. We also calculated the electric field distribution, magnetic field distribution, and multipole decomposition of the two resonances, and the results show that the two modes are ETD resonance and MTD resonance, respectively. The polarization characteristics of these two modes are also investigated, and the average field enhancement factor (EF) of the two modes is calculated. The dynamic modulation of the relative transmission and EF is also achieved based on the tunable properties of the phase change material GSST. Our work provides a way to realize actively tunable TD optical nanodevices.
RESUMEN
In this paper, we performed the ωB97XD/def2-TZVP method with a density functional theory study on the boron-nitrogen (BN) analogues of cyclo[18]carbon. The geometric structure, polarization properties, and excitation effect were calculated in the presence of an external electric field (EEF). Furthermore, the dual descriptor and Fukui function matrices were employed to predict the tendency towards the electrophilic or nucleophilic reactions of B9N9 under varying EEF strengths. The results show that the application of an EEF will cause the cyclic structure of B9N9 to be considerably distorted towards an elliptical geometry, the polarization to increase, and the reactivity of B9N9 to enhance with the increase in the EEF strength. This is of great significance for further experimental exploration into the catalytic properties of BN fullerenes.
RESUMEN
Membrane dipole potential influences a variety of important biological processes involving cell membranes. Because it is quite challenging to directly measure the membrane dipole potential in experiments, molecular dynamics (MD) simulation has emerged as a powerful tool for a reasonable prediction of the dipole potential. Although MD predictions agree well with experiments about the sign of the dipole potential, the magnitude of the dipole potential varies significantly with the force field parameters. It has been shown that the positive dipole potential of phosphatidylcholine (PC) bilayer membranes would be overestimated by a nonpolarizable model owing to the treatment of many-body polarization effects in a mean-field fashion. In this work, we carried out atomistic MD simulations of the diphytanyl PC (ether-DPhPC) and diphytanoyl PC (ester-DPhPC) bilayers and made a comparative study of three different nonpolarizable water models (TIP3P, TIP4P, and TIP5P). Interestingly, we discover that the calculated dipole potential by the TIP5P model shows good agreement with the result obtained using the cryoelectron microscopy experiment, suggesting that a better description of electrostatic interactions in a nonpolarizable water model can effectively ameliorate the overestimation in the calculation of the dipole potential. In addition, our MD results show that the substitution of the ether linkage for the ester linkage of phospholipid bilayers would bring about a change in the orientation of the linkage group with respect to the bilayer normal, leading to the difference in the membrane dipole potential. Surprisingly, although water molecules provide a major contribution to the positive dipole potential, they have a limited impact on the difference of the dipole potential between the ether-DPhPC and ester-DPhPC bilayer membranes.
