There is, I think, something ethereal about i —the square root of minus one. I remember first hearing about it at school. It seemed an odd beast at that time—an intruder hovering on the edge of reality.

Usually familiarity dulls this sense of the bizarre, but in the case of i it was the reverse: over the years the sense of its surreal nature intensified. It seemed that it was impossible to write mathematics that described the real world in …

I and i

Mass production and commercial availability are prerequisites for the viability and wide application of graphene. The exfoliation of graphite to give graphene is one of the most promising ways to achieve large-scale production at an extremely low cost. This review focuses on discussing different exfoliation techniques based on a common mechanical mechanism; because a deep understanding of the exfoliation mechanism can provide fruitful information on how to efficiently achieve high-quality graphene by optimizing exfoliation techniques. We highlight the recent progress on mechanical exfoliation for graphene production during the last decade. The emphasis is set on the widely used sonication method with the latest insight into sonication-induced defects, the newly explored ball milling method, the fluid dynamics method that has emerged in the last three years, and the innovative supercritical fluid method. We also give an outlook on how to achieve high-quality graphene efficiently using mechanical exfoliation techniques. We hope this review will point towards a rational direction for the scalable production of graphene.

A review on mechanical exfoliation for the scalable production of graphene

The fact that a new text book introducing the essentials of computational chemistry contains more than 500 pages shows impressively the grown and still growing size and importance of this field of chemistry. The author’s objectives of the book, using his own words, are “to provide a survey of computational chemistry its underpinnings, its jargon, its strengths and weaknesses that will be accessible to both the experimental and theoretical communities”. This design as a general introduction into computational chemistry makes it an alternative to Andrew R. Leach’s well-established “Molecular Modeling” (Prentice Hall) and Frank Jensen’s “Introduction to Computational Chemistry” (Wiley), although the latter focuses on the theory of electronic structure methods. Cramer’s “Essentials” covers force field and molecular orbital theory, Monte Carlo and Molecular Dynamics simulations, thermodynamic and electronic (spectroscopic) property calculation, condensed phase treatment and a few more topics. Moreover, the book contains thirteen selected case studies sexamples taken from the literature sto illustrate the application of the just presented theoretical and computational models. This especially makes the text book well suited for both classroom discussion and self-study. Each chapter of “Essentials” covers a main topic of computational chemistry and will be briefly described here; all chapters are ended by a bibliography and suggested additional readings as well as the literature references cited in the text. In chapter 1 the author defines basic terms such as “theory”, “model”, and “computation”, introduces the concept of the potential energy surface and provides some general considerations about hardware and software. Interestingly, the first equation occurring in the text is not Schro ̈dinger’s equation, as is the case for most computational chemistry introductions, but the famous Einstein relation. The second chapter deals with molecular mechanics. It explains the different potential energy contributions, introduces the field of structure optimization, and provides an overview of the variety of modern force fields. Chapter 3 covers the simulation of molecular ensembles. It defines phase space and trajectories and shows the formalism of, and problems and difference between, Monte Carlo and molecular dynamics. In chapter 4 the author introduces the foundations of molecular orbital theory. Basic concepts such as Hamilton operator, LCAO basis set approach, many-electron wave functions, etc. are explained. To illuminate the LCAO variational process, the Hu ̈ckel theory is presented with an example. Chapter 5 deals with semiempirical molecular orbital (MO) theory. Besides the classical approaches (extended Hu ̈ckel, CNDO, INDO, NDDO) and methods (e.g., MNDO, AM1, PM3) and their performance, examples are provided from the ongoing development in that still fascinating area. Ab initio MO theory is presented in chapter 6; the basis set concept is discussed in detail, and, after some considerations from an user’s point of view, the general performance of ab initio methods is explicated. The next chapter covers the problem of electron correlation and gives the most prominent solutions for its treatment: configuration interaction, theory of the multiconfiguration self-consistent field, perturbation, and coupled cluster. Practical issues are also discussed. Chapter 8’s topic is density functional theory (DFT). Its theoretical foundation, methodology, and some functionals as well as its pros and cons compared to MO theory are presented together with a general performance overview. The next two chapters deal with charge distribution, derived and spectroscopic properties (e.g., atomic charges, polarizability, rotational, vibrational, and NMR spectra), and thermodynamic properties (e.g., zero-point vibrational energy, free energy of formation, and reaction). The modeling of condensed phases is addressed in chapters 11 (implicit models) and 12 (explicit models), which closes with a comparison between the two approaches. Chapter 13 familiarizes the reader with hybrid quantum mechanical/molecular mechanical (QM/MM) models. Polarization as well as the problematic implications of unsaturated QM and MM components are discussed, and empirical valence bond methods are also presented. The treatment of excited states is the topic of chapter 14; besides CI and MCSCF as computational methods, transition probabilities and solvatochromism are discussed. The last chapter deals with reaction dynamics, mostly adiabaticskinetics, rate constants, reaction paths, and transition state theory are section topics here sbut also nonadiabatic, introducing curve crossing and Marcus theory in brief. The appendix is divided into four parts: an acronym glossary (which is very helpful), an overview of symmetry and group theory, an introduction to spin algebra, and finally a section about orbital localization. A rather detailed index ends the book. The “Essentials” writing style fits the fascinating topic: one reads on and on andssurprise! sanother chapter has been absorbed. The text is complemented by a large number of black and white figures and clear tables, mostly self-explanatory with descriptive captions. The use of equations and mathematical formulas in general is well-balanced, and the level of math should be understandable for every natural scientist with some basic knowledge of physics. There are only a few minor shortcomings: for example, a literature reference cited in the text (“Beck et al.”, p 142) is missing in the bibliography; “Kronecker” is mistyped with o ̈; and the author completely forgot to reference Leach’s text book when referring to other computational chemistry introductions. However, the author has established a specific errata web page (http://pollux.chem.umn.edu/ ∼cramer/Errors.html) with all known errors. These will be corrected in the next printing or next revised edition, respectively. With its emphasis, on one hand, on the basic concepts and applications rather than pure theory and mathematics, and on the other hand, coverage of quantum mechanical and classical mechanical models including examples from inorganic, organic, and biological chemistry, “Essentials” is a useful tool not only for teaching and learning but also as a quick reference, and thus will most probably become one of the standard text books for computational chemistry.

Essentials Of Computational Chemistry Theories And Models

https://www.thelancet.com/pdfs/journals/lancet/PIIS0140-6736(12)60071-3.pdf

Androgen insensitivity syndrome

on the use ofmicrowaveirradiationto“accelerate”organicchemicaltrans-formations, there has been considerable speculation anddiscussion of this effect. Much of the debate has centeredaround the question whether the observed effects can in allinstances be rationalized by purely thermal/kinetic phenom-ena (thermal microwave effects) arising from the rapidheating and high bulk reaction temperatures attained withmicrowave dielectric heating, or whether some effects areconnected to so-called specific or nonthermal microwaveeffects.

Microwave Effects in Organic Synthesis: Myth or Reality?

In an experiment in which two or more photoevents arriving at the same pixel are considered as a single count, a one-pixel-sized central hole appears in the autocorrelation estimate. This hole is a source of error when high-resolution techniques based on the autocorrelation function are applied to image or signal recovery. We present an experimental method with which to evaluate the autocorrelation central hole based on the simultaneous measurement of the total number of counts in the image detector and an auxiliary photomultiplier. The technique is easy to perform and provides high accuracy.

Autocorrelation hole in nonlinear image detectors: an estimate using an auxiliary photomultiplier.

Correction for 'Understanding MAOS through computational chemistry' by P. Prieto et al., Chem. Soc. Rev., 2017, 46, 431-451.

/pdf/correction-understanding-maos-through-computational-53ao60g0ez.pdf

Antonio M. Rodríguez

Papers

Autocorrelation hole in nonlinear image detectors: an estimate using an auxiliary photomultiplier.

Correction: Understanding MAOS through computational chemistry