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Density functional theory (DFT) has become ubiquitous for chemical applications in research and in education. The exact functional at the foundation of DFT is unfortunately unknown, and issues arise when choosing an approximation for a specific application. With this tutorial review, we tackle the selection problem and many related ones, such as the choices of a basis set and of an integration grid, that are often overlooked by occasional practitioners and by more experienced users as well. We offer a practical approach in the form of a commented notebook containing 12 experiences that can be run on a simple computer in just a few hours. We propose this review as a primary source for those who are willing to include DFT in their everyday research or teaching activities in a way that reflects the research advances of the field in the last couple of decades. [ABSTRACT FROM AUTHOR]

The importance of databases of reliable and accurate data in chemistry has substantially increased in the past two decades. Their main usage is to parametrize electronic structure theory methods, and to assess their capabilities and accuracy for a broad set of chemical problems. The collection we present here—ACCDB—includes data from 16 different research groups, for a total of 44,931 unique reference data points, all at a level of theory significantly higher than density functional theory, and covering most of the periodic table. It is composed of five databases taken from literature (GMTKN, MGCDB84, Minnesota2015, DP284, and W4‐17), two newly developed reaction energy databases (W4‐17‐RE and MN‐RE), and a new collection of databases containing transition metals. A set of expandable software tools for its manipulation is also presented here for the first time, as well as a case study where ACCDB is used for benchmarking commercial CPUs for chemistry calculations. © 2018 Wiley Periodicals, Inc. ACCDB—A Collection of Chemistry DataBases—includes five previously published databases from different sources (GMTKN, MGCDB84, DP284, Minnesota2015B, and W4‐17), and three new one (W4‐17‐RE, MN‐RE, and Metals&EE), and it includes 44,931 unique reference data (all at a level significantly higher than DFT), and 10,049 structures. Software tools for manipulation of ACCDB are also presented, as well as a case study for the performance of commercial CPUs for quantum chemistry calculations. [ABSTRACT FROM AUTHOR]

• Helical-chiral imidazopyridine-2-yilidenes were synthesized from 2-aza[6]helicene. • Energies of their frontier orbitals were analyzed by the density functional theory. • Helicene annelation lowered the energy of π-acceptor orbital by 1.47 eV. Helical-chiral analogues of imidazopyridine-2-yilidene were synthesized from 2-aza[6]helicene. The energies of their frontier orbitals were analyzed by the density functional theory calculations. The exceedingly large extension of NHC's π system by helicene annelation significantly enhanced the π electron-accepting properties of the carbene center while the strong σ electron-donating properties of imidazopyridine-2-yilidenes were retained. [ABSTRACT FROM AUTHOR]

Isolated, bench-stable, non-symmetric diarylmethylium salts have been reacted with cyclic silyl enol ethers. Products have been easily obtained in a prevalent diastereoselectivity irrespective of salt counter-anion, aromatic ring substitution and silyl enol ether ring size. X-ray analyses on two purified diastereomers have been performed; the observed diastereoselectivity has been confirmed and rationalised using DFT calculations. [ABSTRACT FROM AUTHOR]