Ab initio vibrational and thermodynamic properties of adamantane, sila-adamantane (Si10H16), and C9Si1H16 isomers

Theoretical Study of Si/C Equally Mixed Dodecahedrane Analogues

To gain insight into the effect of Si/C arrangement on the molecular framework of strained polyhedral compounds, dodecahedrane analogues containing equal numbers of carbon and silicon (Si/C equally mixed dodecahedrane analogues) were investigated using the ab initio molecular orbital method. There are 1648 isomers for which the Si/C arrangement on the molecular framework is different. Based on the geometry optimization of all the isomers as well as the carbon and silicon analogues, the characteristics of the structure, relative energy, and strain energy of the Si/C equally mixed compounds are presented. Then, important factors controlling the relative energy, such as strain energy, are proposed through regression analysis. Also discussed is the correlation between the relative energy and the indices of Si/C dispersion, such as the number of skeletal C-Si single bonds and condensed five-membered rings constituting the polyhedral structure.

Bond order effects on the optoelectronic properties of oxygen/sulfur functionalized adamantanes

The objective of this work, is to study adamantanes and to tune their bandgap, since pure adamantane is considered as an insulator due to its high bandgap energy. For this, we doped adamantane with oxygen and sulfur atoms, thus obtaining 730 different structures with double bonds and 730 different structures with single bonds, for a total of 1460 structures, and compared their properties. Among all, 31 molecules were selected that best represented the reduced bandgap behavior. The calculations with greater precision in its results were made using the Local Density Approximation (LDA), in the Density-Functional Theory (DFT) formalism, with PWC functional and TNP basis set. The electronic and optical properties were analyzed, by calculating the energy gap and absorption spectrum. Importantly, we observed that molecules doped with sulfur atoms (double bonds) had their energy gap reduced significantly compared to molecules doped with sulfur and/or oxygen atom with single bonds and pristine adamantane. It was found that in the absorption spectrum, the sulfur-doped structures had their spectrum shifted to the visible region, a fact that becomes relevant for potential dyes and optoelectronic applications. From the seven selected functionalized adamantanes (ADD-04, ADD-05, ADD-07, ADD-19, ADD-20, ADD-41, and ADD-48), any of these could be used as a dye. However, the ADD-20 molecule in particular, which presented optical absorption near (RGB) primary colors, could indicate a potential quantum dot material for application in developing screens of various electronic devices.

Cubane and cubanoid: Structural, optoelectronic and thermodynamic properties from DFT and TD-DFT method

In this paper, we report structural, electronic and optical properties of cubane (C₈H₈) and cubanoids (cubane-like molecules) using Density Functional Theory (DFT). The cubanoids are cubanes for which Carbon atoms have been substituted by Nitrogen (N), Phosphorus (P), Boron (B), Silicon (Si), Arsenic (As), Antimony (Sb) or Bismuth (Bi) atoms. These molecules presented exceptional stability with several different symmetry point groups, being the majority T_d. All calculated vibrational frequencies are positive for any studied molecules indicating that all these structures are in a stable state. The HOMO-LUMO gaps and DOS were calculated converged towards to values between 1.87 eV and 5.61 eV, actually showing promising electronic properties (Just for comparison, the cubane energy gap is 7.50 eV). The optical absorptions were also calculated for the cubanoid structure using the Time-Dependent Density Functional Theory (TD-DFT). Their dependence on the wavelength is analyzed, where five of theses structures absorb on the visible region. Finally, the extrapolation of thermodynamic properties indicates that these cubanoid could be potentially synthesized spontaneously, where four structures, the synthesis would occur for temperatures below 400 K, while for Si₄Bi₄H₄ structure, the synthesis would occur at room temperature.

Recent advances in hybrid measurement methods based on atomic force microscopy and surface sensitive measurement techniques

This review summaries the recent progress of the combination of optical and non-optical surface sensitive techniques with the atomic force microscopy.